Exactly how old is he? It sounds like he may be going through puberty. Aggression toward humans is pretty rare in beardies, but the one time they are likely to act like this, as far as I am aware, is when they are juvenile males going through puberty. It's probable, also, that you are doing something to frighten him. Beardies generally do not bite except to defend themselves and to drive off rival males when they want to mate. So either he sees you as a rival male that needs to be put in his place, or he thinks you're a predator and he's trying to defend himself. If it's puberty, you're in luck -- he'll grow out of it once he's through his hormonal stage. If he's afraid of you, on the other hand, there are things you can do to make yourself less fearsome.
I also have to wonder, how much are you feeding him and how often? And what? I handfeed my beardie and once or twice he has bitten my hand by accident when going for food. If you have ever handfed your beardie, and he is very hungry, he may rush your hand in excitement and bite at it, thinking you are holding food. Mine has never been so hungry as to charge me so aggressively that he missed the food and bit me, but I let mine gorge himself daily, and, of course... I'm actually holding food when this happens.
How long have you owned this lizard, also?