The attackers sprayed bullets into the mosque in the home village of Kano governor Rabiu Musa Kwankwaso.
His elderly father was in the mosque, but escaped unhurt, witnesses said.
No group has said it carried out the attack but one of Mr Kwankwaso's aides said it was punishment for his recent defection from the governing party.
Islamist group Boko Haram has also staged several attacks in Kano and elsewhere in northern Nigeria.
The run-up to elections in oil-rich Nigeria is often marred by violence between rival political groups.
Mr Kwankwaso was among five influential governors who defected from President Goodluck Jonathan's People's Democratic Party (PDP) to the opposition All Progressives Congress (APC) in November.
Heshimu Suleiman, a special assistant to the governor, said the attack was politically motivated to punish Mr Kwankwaso for defecting, reports the AP news agency.
The PDP has not yet commented on the allegation.
In December, Nigeria's ex-President Olusegun Obasanjo said it would be "morally flawed" for Mr Jonathan to seek re-election next year.
He said Mr Jonathan had failed to tackle Nigeria's many problems, including corruption and an insurgency led by the militant Islamist group Boko Haram.
Mr Jonathan defended his record in government, but has not yet declared his candidature.
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