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."
Liverpool looked comfortable after Ngog's well-struck early volley but things started going wrong after 26 minutes when Christian Benitez levelled for Birmingham.
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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.
"I haven't seen the replay but maybe it wasn't a penalty," Benitez told BBC radio. "It's possible but we have had a lot of situations this year against us.
"We had lots of possession and loads of attempts at goal and it was unbelievable we were losing 2-1 at half-time. But the team showed a lot of character.
"Gerrard was available but not 100 percent fit. But he has the quality and passion that we needed," added Benitez who sent on midfielder Alberto Aquilani late in the game for his first Premier League action since joining from AS Roma in August.
Injuries to Albert Riera and Yossi Benayoun added to Liverpool's problems, both suffering hamstring problems.
