Substitute Gerrard, who has been nursing a groin injury, came on late in the first half and equalised with 19 minutes remaining after Lee Carsley was harshly adjudged to have brought down David Ngog, scorer of the opening goal.
“It's a joke. I know for a fact I didn't touch him,” Carsley told ESPN. “I think when the referee (Peter Walton) sees it, he'll be really disappointed.”
Television replays appeared to show Carsley, who was booked for protesting, made no contact with Ngog.
Liverpool looked comfortable after Ngog's well-struck early volley but things started going wrong after 26 minutes when Christian Benitez levelled for Birmingham.
Worse was to follow for the home team seconds before half time when Cameron Jerome unleashed a swerving effort past ‘keeper Pepe Reina from 30 metres.
Seventh-placed Liverpool, without the injured Fernando Torres, mounted constant pressure after the break but had to be content with their first draw of the season, which leaves them 11 points behind leaders Chelsea.
Under-pressure manager Rafa Benitez agreed the penalty, which spared his side a sixth league defeat of the season, looked harsh.
“I haven't seen the replay but maybe it wasn't a penalty. It's possible but we have had a lot of situations this year against us,” Benitez told BBC radio.
