Earlier, police told The Washington Post that one police officer and eight civilians were killed in the blast. The explosion reportedly rocked the mosque during Friday evening prayers.
The blast took place in the Ghousabad neighbourhood of Quetta on late Friday and left 20 more people injured, the Geo TV broadcaster reported.
The authorities have launched an investigation into the incident.
In October, at least one policeman had been killed and five others seriously injured in a major blast in the Quetta region. A local official said that the target of the blast was a mobile police van.
Pakistan has been targeted by a number of attacks conducted by rebels in the area.