For me, the anger is the "fight" option of the "fight-or-flight" reponse to anxiety. There's a lot of adrenaline involved with anxiety and in my case it can definitely cause aggression.
Breathing exercises, meditation, and putting down caffeine have helped me a lot. I also do 900mg of St John's Wort herbal (OTC) every day. My PCP says that there is significant anecdotal evidence that St. John's helps with anxiety and he supports it.