The rules for Frenzy state "The character must attack the nearest enemy in melee combat if possible" and that if not engaged he must move towards the nearest enemy.
This seems pretty clear cut to me that, while Frenzied, the character can do nothing on his turn but advance and make melee attacks.
So how does the Mental Rage talent work? It says that while in a Frenzied state "the character may use his psychic powers normally." Does this override Frenzy's compulsion to move or attack in melee? Does he then have the option to either advance and attack OR cast/sustain whatever powers he wants during his turn?