Firefighters were called to the set in the BBC's Elstree studios in Hertfordshire just after 23:00 GMT on Tuesday.
Flames were reported in parts of a building on Albert Square.
A firework is believed to have caused the fire, which did not lead to serious damage.
The blaze, which was in the first floor and roof space of the building, was soon "contained and extinguished" by crews, said Ian Parkhouse from Hertfordshire fire and rescue service.
"We're pleased that we were able to deal with this incident quickly, so it shouldn't affect the 30-year celebrations taking place this week," he said.
A spokeswoman for the soap said: "There was a very small fire on set on Tuesday night after rehearsals had finished.
"It has not affected any #EELive week plans and nobody was harmed," she added.
The show is broadcasting live inserts in all its episodes this week, and will screen a fully live episode on Friday to celebrate its anniversary.

Duffy, 37, has joined the third-placed Championship side on a one-year contract after leaving Swinton Lions.
The Scotland assistant coach will lead Featherstone in their final league game against Toulouse on Saturday before the upcoming Super 8 Qualifiers.
"He is a fantastic coach and we are very excited to see how his reign here unfolds," chairman Mark Campbell said.
"We believe he has done a remarkable job in extremely difficult circumstances at Swinton and he deserves a great deal of credit for his efforts there."
Duffy, who played for Leigh, Widnes and Salford during a 16-year playing career, has been replaced by his former assistant Stuart Littler at fellow Championship side Swinton.

Greater Manchester Police (GMP) apologised for racial stereotyping for using a fake terrorist shouting "Allahu Akbar" in the mock terror attack.
Organisers of the meeting at Longsight Saath Saath are demanding an inquiry.
GMP said it has no plans to issue any further statements on the training exercise staged at the Trafford Centre.
The scenario for the mock suicide bombing was by an extremist Daesh-style organisation although GMP had said the event was not linked to any specific terror threat.
Syed Azhar Shah, who chaired the meeting attended by about 30 people, said GMP assistant chief constable Garry Shewan's apology was not enough and "only acceptable" if those responsible resigned.
He said while the training exercise was a good idea but it was "shocking to portray Muslims as terrorists" and that only one group would commit terrorist acts.
He said: "It is also shocking what our children and community who live in this country will see themselves as; terrorists or British citizens?"
Mr Shah said further events would be held to "condemn this" and "ensure this would not happen again".
He said one apology "would not mend so many hurts".
One of those at the meeting said using a Muslim as a terrorist sent out "the totally wrong message" and "puts a wedge" between the community and GMP.
"We are all British citizens. As far as Islam is concerned it does not permit any killing."
Greater Manchester's police and crime commissioner Tony Lloyd, said it was "frustrating" the operation had been "marred by the ill-judged... and unacceptable decision" to have the terrorist shout 'Allahu Akbar' before setting off fake bombs.
Other locations in the three-day counter-terrorism exercise include Redbank Community Home in Newton-le-Willows.
A fire broke out on the set of EastEnders a few hours after the BBC soap broadcast "live inserts" as part of 30th anniversary celebrations.
[NEXT_CONCEPT]
Featherstone Rovers have appointed John Duffy as head coach following the departure of Jon Sharp.
[NEXT_CONCEPT]
Police have been accused of "institutional racism" for portraying a suicide bomber as an Islamist terrorist, a protest meeting heard.