The car blew up with a loud bang at Baramkhel area in Lakki Marwat, located near Dera Ismail Khan city, where a suicide attack on Friday on a Shia funeral procession left 32 people dead.
Four passers-by were killed by the explosion, TV channels reported. Witnesses said they had seen parts of bodies lying strewn near the car, which was completely destroyed by the blast.
Police officials said the suicide attacker's vehicle had apparently blown up before he could reach his intended target.
Meanwhile, a tense calm prevailed in Dera Ismail Khan, where curfew was imposed after violent protests erupted following the suicide attack on the funeral procession. The army has also been deployed in the city.
The funeral of most of the people killed was held amidst tight security on Saturday morning. Security forces continued patrolling the city.