Circular formation around the moon I have seen a large circular formation of cloud around the full moon sometimes.

Have anyone seen the same? What is the reason behind this formation?
Due to lunar attraction?

Most of the sky is empty and clear, and no clouds at all, only around the moon, far from the moon, not just very close, that cloud circle formed. 
I saw this many times, like the below drawing:
That sounds very much like a 22° halo.

It's not an astrophysical phenomenon; it results from the refraction of light by ice crystals in Earth's atmosphere.

If this is what it is, it should be a fuzzy but regular circle centered on the Moon, with a radius of about 22 degrees. If you hold your fist out at arm's length with the thumb extended, the angular distance between the base of your fist and the tip of your thumb is typically close to 15 degrees; you can use that for visual comparison. Remember that 22° is the radius of the halo; the diameter is 44°, close to three time the width of your fist+thumb.