Four people were reportedly killed in the explosion which happened just after Friday prayers.
Islamist sect Boko Haram - which killed 42 with a series of Christmas Day bombs outside churches - has been blamed. The city is known to be its stronghold.
One resident said: 'There was a loud blast near the mosque just after the Friday prayers as people were trooping out of the mosque.
'Everybody scampered to safety, leading to a stampede.'
Army spokesman Brigadier General Isa initially blamed Boko Haram for the attack, but it is not yet known if and why it would attack a mosque. Read More