Adobe Illustrator draws multiple shapes while drawing single shape
Well, This usually happens when using the Tilde (~) key.
It's a "Continuous Duplicates Based on Mouse Movement" function and combined with Alt/Option, Shift/Command and spacebar you can create new and complex effects.
Are you sure your Tilde key is not pressed or locked somehow? Also, try drawing a circle while holding the Tilde key pressed...
I'm asking cause I don't know of a setting in Illustrator that will do this automatically...
PS: Here's an article where you can read about it.