Aggression is verbal or physical behavior intended to cause harm. It is difficult to think that we participate in aggressive behavior, and yet we all do at some level and at some point in our lives. The Social Learning Theory presents agression as a learned behavior. The Frustration Agression Theory is the theory that agression causes frustration and frustration cause anger and hostility and triggers a readiness to aggress.
In my opinion, the social learning theory is more persuasive, though I can see merit in both theories.
I do certainly believe that being frustrated causes us to feel aggressive. I know from thinking about my own behaviors and feelings that I can act in less controlled ways when I feel frustrated.
However, these feelings of frustration do not necessarily cause me to act out. I think that how we act when frustrated is, in large ways, learned. I think that we model ourselves after those we see as we grow up -- we learn from them how to deal with frustration.
So I think that frustration certainly does cause aggression, but that it only does so if we have not properly learned (while being socialized) how to deal with frustration.