Rents for grade A offices have risen to £15.50-per-sq ft over the past year, according to commercial agents.
But they are still well below the UK average of £24.
It is claimed that the prospect of a relatively low financial return is acting as a barrier to substantial build projects.
In March, an Invest NI report said there is a shortage of grade A space office in Belfast.
Grade A offices are classed as new or refurbished buildings, in prime locations, with open-plan layouts.
Ian Duddy of Colliers International in Belfast said: "The shortage of grade A space in Belfast has led a number of major occupiers to develop their own headquarter buildings.
"Further rental growth in the grade A market is necessary to encourage new development in the city."
Office development has slowed since the 2008 property market crash.
Loans of public money could soon be made available to property developers to help them build offices, after a recent report for Invest NI described supply as "extremely limited".
Invest is exploring whether to advance loans as "a short-term intervention".

Mark Jones, 45, of Cwmbran, Torfaen, fractured Amelia Jones's skull when he was supposed to be looking after her.
He had denied murder but was convicted at Newport Crown Court on Thursday and jailed for life.
He was also jailed for four years after admitting perverting the course of justice which will be served concurrently.
Mr Justice Wyn Williams said Jones had shown no remorse for his "wicked and despicable" actions.
He said: "It may well be that you are never released from prison or if you are, you will be a very old man."
The court heard he had "totally destroyed" the life of his daughter, Sarah Jones, and given her surviving children nightmares.
A victim impact statement from Ms Jones, said: "It really upsets and saddens me now, looking back, I spent such little time with her.
"It seems like she didn't really exist, like she was some kind of dream."
The court was told the rest of her children were taken from her for about 18 months, between November 2012 and April 2014.
One child in particular was "afraid his grandfather would kill him if he got out of prison", the statement said.
"There have been times when I blamed myself for what happened to Amelia, because I was the person who invited him back into my life," Ms Jones added.
"As far as I'm concerned he is no longer my father."
Amelia died in November 2012 after suffering a "catastrophic" bleed to the brain.
During his trial, Jones claimed he fell with Amelia in his arms on one occasion and passed out while holding her on another.
But the court heard she had suffered a skull fracture, brain swelling and multiple rib fractures and had been injured at least three different times.
The prosecution said the injuries "could not have been accidental" and were all deliberately inflicted by her grandfather, who frequently had sole charge of Amelia.
The prosecution said he hurt her because he disliked her father, Ian Skillern.

The IMF's steering committee, made up of 25 of the world's largest economies, said the global outlook was fraught because of weak trade and a series of risks including a UK exit from the EU.
It urged countries to boost public spending and avoid deflation.
The IMF last week made its second cut to global growth forecasts this year.
Christine Lagarde, managing director of the IMF, described the talks between finance ministers and central bankers in Washington DC as "collective therapy" to deal with the gloomy prospects.
But she said calmer financial markets since February had reduced the nerves at the IMF spring meeting.
"There was not exactly the same level of anxiety but I think there was an equal level of concern, and a collective endeavour to identify the solution and the responses to the global economic situation," she said.
The IMF now predicts global growth of 3.2% this year and 3.5% in 2017, having previously forecast 3.4% and 3.6% respectively.
"Downside risks to the global economic outlook have increased since October, raising the possibility of a more generalised slowdown and a sudden pull-back of capital flows," the IMF steering committee said.
It said countries' tax policies and public spending should be "as growth-friendly as possible".
But it also pledged to "refrain from all forms of protectionism and competitive devaluations", amid concerns that some countries are keeping their currencies weak to boost exports.
Rents for premium office space in Belfast city centre have risen by 19%, but experts say still not enough to generate a boom in developments.
[NEXT_CONCEPT]
A man who murdered his five-week-old granddaughter has been jailed for life and will serve a minimum of 25 years.
[NEXT_CONCEPT]
Key countries in the International Monetary Fund (IMF) have pledged to pursue "growth-friendly" policies to kickstart the slowing world economy.