Gerrard, a second half substitute, struck with 20 minutes remaining after Lee Carsley was harshly adjudged to have brought down David Ngog, scorer of Liverpool's opener.
Liverpool looked comfortable after Ngog's well-struck early volley but were stung when Christian Benitez touched in an equaliser for Birmingham after 26 minutes.
Worse was to follow for Liverpool seconds before halftime when Cameron Jerome unleashed a swerving effort past keeper Pepe Reina.
Liverpool, in seventh place, 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.
(Reporting by Martyn Herman, editing by Tony Jimenez)