The bomb exploded at the entrance of Saleh mosque, located close to the Arambagh police station, when people were coming out after prayers.
"It (the bomb) was detonated with a remote control and so far we know that a person has been killed and around 13 injured in the blast," DIG South Sheikh said adding the injured included a woman.
This is the first time that a bomb attack has been carried out at a mosque of the Bohra community in Karachi.
Panic and fear spread in the busy commercial area immediately after the blast.
Karachi, a city of 18 million, is rife with criminal, ethnic, political and sectarian killings which claim hundreds of lives each year.
In recent times extremist Sunni Muslim groups have carried out suicide bomb attacks on Shia Muslims.
