They struggled to overcome the Royals in a game which only came to life in the final ten minutes when both teams converted penalties.
Hungary international Zoltan Gera converted Albion's 81st minute spot-kick only for Kevin Doyle to equalise with a penalty two minutes later.
Reading, beaten only twice this season by Plymouth and Arsenal, proved that their credentials are of the highest order with their latest performance.
To earn a replay was no mean achievement but it was well-merited on this occasion as Albion struggled to make an impact.
The Royals, unbeaten in 27 games, gave another good account of themselves despite manager Steve Coppell only including five of his regular first team.
They went into the game with a record of being the only team in the two top divisions without an away defeat in the League and they demonstrated their confidence with some skilful and confident play.
Steve Sidwell, the former Arsenal defender, was again a key performer but Reading missed Irishman Kevin Doyle, who has been a revelation this season since his arrival form Cork, in a goalless first half.
Reading's defence was again solid as expected from a rearguard which has only conceded 14 goals in 27 league games this season.
Considerable pressure was exerted by Albion at the start of the second half when Kanu finally produced a shot but it was just off target.
But there were still a lot of question-marks to be asked about a lack-lustre Albion side. The response was to send on both Geoff Horsfield and Kevin Campbell for Junichi Inamoto and Nathan Ellington in the 53rd minute.
Ominously Albion still struggled to raise their game as Reading continued to frustrate the Premiership side.
Coppell decided to bring Doyle into the action in an attempt to snatch a surprise win. They kept at their task and forced Chris Kirkland into making several smart saves.
Their best chance of taking the lead fell to Steve Hunt but Kirkland, who has high hopes of going to Germany for the World Cup finals, had no trouble making a comfortable save.
The belated introduction of Gera sparked Albion to life and his cross into the middle resulted in Horsfield being fouled by Chris Makin in the 81st minute.
But two minutes later Reading were back on level terms when Martin Albrechtsen handled and substitute Doyle converted his spot-kick to earn a replay a week on Wednesday.
West Brom - Curtis Davies. Ensured the Championship side were restricted to a handful of scoring opportunities in a tame affair.
Reading - Steven Sidwell. Showed that Steve Coppell can afford to rest Kevin Doyle with little detriment to the engine room of the Royals midfield.