Gerrard, who came off the bench following a groin problem, rescued a point after Ngog went down under Lee Carsley's challenge, with furious City players insisting the French striker had dived.
Despite the recovery, Liverpool remain seventh in the table -- 11 points behind leaders Chelsea to increase the pressure on manager Rafael Benitez.
Liverpool went into the game on the back of six defeats in eight matches but they took a 12th minute lead when Ngog fired in a powerful left-foot volley after Albert Riera had lobbed the ball into the area.
But, midway through the first half, Birmingham drew level from when a James McFadden free-kick was headed on by both Roger Johnson and Scott Dann for Christian Benitez to head past Jose Reina from close range for his first Birmingham goal.
The visitors then stunned the home fans by taking the lead on the stroke of half-time when Cameron Jerome thumped home from 30 yards out after he latched onto Dann's headed clearance.
Liverpool poured forward and Steven Gerrard almost made a dramatic impact, meeting Glen Johnson's cross only for his header to glance the outside of the post.
Then, after earning the penalty, Ngog almost stole the winner with a near-post effort from Gerrard's cross -- but failed to hit the target from close range.