A regional official confirmed the bombing in the village of Payee Khan, in the troubled Mohmand region of the lawless Federally Administered Tribal Areas (FATA) bordering Afghanistan.
"The suicide bomber was in crowded mosque," Naveed Akbar, deputy administrator of Mohmand agency, told Reuters.
Shaukat Khan, another official in the northwestern FATA region, said at least 24 people were wounded.
"Many people were gathered inside the mosque where a suicide bomber blew himself up," he said.
Pakistan's frontier regions, which are deeply conservative and hard to access due to rough terrain, have long been the sanctuary of fighters from al Qaeda, the Taliban and other terrorist groups.