At least 22 other people were seriously injured when the blast happened during Mass, around 9 a.m. local time, The (Nigerian) Daily Trust reported.
Apart from the bomber, the other fatalities were a woman and child, China's Xinhua news agency reported.
While no group immediately claimed responsibility for the attack in the predominantly Muslim region, Voice of America reported it bore resemblances to previous attacks by the Islamist fundamentalist Boko Haram militant sect.
The group's members don't recognize the federal government or constitution and demand a "pure" Islamic state in the north.
The last time the group attacked a Catholic church in Bauchi was June 3, when 12 people were killed by a bomb, the report said.