N.R.
Aleisha,
Unless your child is showing other signs of autism (anti-social, does not make eye contact, speaks very little) i wouldn't worry. They say this could be a sign of high intelligence as well. My husband used to bang his head on the wall when he was a child and now he has a PhD in poylmer science! Your son might also be doing it to get attention, especially if you respond to it all of the time.
N.