The ritual of lichdom that you undertook did not transform you into an undead monstrosity. Instead, you appear much like a normal human and have mastered moving amongst the living. Only the closest of examination (for example, you have no heart beat) will reveal you for what you truly are.
You can temporarily drop the disguise as a swift action and reveal your true nature. Only then does your fear aura special attack become active. Restoring the illusion of normality is a full-round action.
Way of the Wicked Book Five — The Devil My Only Master. Copyright 2012, Fire Mountain Games LLC; Author: Gary McBride.