The bomb went off in the main bazaar of Miranshah, the main town in North Waziristan district, a security official said.
Witnesses and hospital officials said 11 people had been taken to Miranshah Civil Hospital, some of them in a serious condition.
Another official in the northwestern city of Peshawar confirmed the blast and the casualties.
No one has claimed responsibility for the blast.
Pakistan goes to the polls on Saturday to elect a new government, the first time in the country's turbulent history that one civilian administration has handed power to another through the ballot box.
But the campaign has been marred by violence, with more than 100 people killed in bombings and shootings in the month leading up to polling day.
May 10, 2013 - Updated 1055 PKT