The bomb was detonated by remote control near the stadium in Jamrud, one of the main towns of Khyber tribal agency, an official, Jamil Ahmad, told reporters.
The car was parked at a workshop in a busy market.
Some officials said the attackers may have intended to target the stadium, where a religious party was scheduled to hold a rally tomorrow.
Footage on television showed several cars were destroyed by the explosion.
No group claimed responsibility for the attack though authorities usually blame militants for such incidents.
The Khyber tribal agency, which borders Afghanistan, was a key supply route for NATO forces in the war-torn country.
