Simon Church had bundled in an opener to give the hosts the scent of an upset but Gerrard levelled before the break for Rafael Benitez's men.
Liverpool had been defeated on their last visit to Reading's stadium, little more than two years ago, but plenty has changed since the days of Steve Coppell's men upsetting the heavyweights in the Premier League.
The Royals head back into Championship action sitting just above the relegation zone in 20th place and there is a feeling of frustration from fans against chairman Sir John Madejski, who is yet to appoint a new manager following Brendan Rodgers' dismissal last month.
Reading chief scout Craig McDermott has been in charge and while survival is the priority, a run in the FA Cup tends to boost confidence.
They also had Brian Howard, who scored a famous winner for Barnsley against the Reds in 2008, on the bench after a jaw injury.
Liverpool's season has seen them knocked out of the Champions League and also struggle to keep pace with others teams in the hunt for a top-four place in the Premier League, so the cup has been seen as one of their only genuine chances of success.
With that in mind, Benitez picked a strong team - Gerrard and Fernando Torres started - but they started poorly, not helped by the tricky conditions at Reading's ground, a venue that also hosts rugby games for London Irish.
The hosts had the ball in the net when Jobi McAnuff met Pepe Reina's punch but the header was correctly ruled out as Grzegorz Rasiak was offside and also impeded the Liverpool goalkeeper to allow the finish to trickle over the line.
Reading goalkeeper Adam Federici was fortunate to escape further punishment when he handled outside the penalty area, claiming a ball Gerrard pushed through to Fabio Aurelio. Martin Atkinson only awarding a free-kick.
The West Yorkshire referee was also lenient when he turned down a Reading appeal for a penalty when Martin Skrtel tugged on Gylfi Sigurdsson's shirt, but Emiliano Insua finally went in the book when he fouled McAnuff on the right flank.
That led to Church's strike. Ryan Bertrand swung over the deep free-kick to the far post, with most Liverpool players expecting the ball to drift out of play.
They did not count on Rasiak darting around Lucas Leiva and pulling the ball back from the byline. Church used his shins to tap in from close range for his fifth goal of the season.
Liverpool looked to Torres to get them back in the game and the Spain striker headed just wide when Dirk Kuyt crossed from the right channel.
It was their other talisman, Gerrard, who grabbed the equaliser. The midfielder picked the ball up 25 yards from goal and shaped to cross, with Kuyt stepping over the delivery to fool Federici.
Gerrard sent Torres through before the break and Federici spread himself well to block the finish, and Aurelio also drilled wide when sent through.
Reading's disgruntled fans spotted their former manager on his duties as a pundit and chanted "we want our Coppell back", as they hope for a return to the days of success.
The club have been in freefall since relegation from the top flight two seasons ago and the likes of Kevin Doyle and Stephen Hunt have been sold - but at least the current players were not giving up. Sigurdsson unleashed a swerving shot that required a decent Reina save.
Torres had threatened just after the break when he went just over the crossbar from the edge of the area.
Federici appeared to pull a hamstring midway through the second half, so Ben Hamer came off the bench and saved on the line from Alberto Aquilani before the end. Torres headed just over in stoppage-time.