A police officer and four civilians died in the attack in Doaba town in Khyber Pakhtunkhwa province, 30 kilometres (18 miles) from Hangu district, senior local police official Abdul Rashid told AFP.
"The bomber, riding an explosive packed car, blew himself up near a police station, killing five people and wounding 25 others," Rashid said.
The bomber had been aiming to strike the building but failed to do so because of barricades that had been erected outside, he said.
Part of the police station was still completely demolished by the blast, Rashid added, with the impact also damaging at least 10 nearby houses.
"No one has so far claimed responsibility for the incident," Rashid said.
Another senior local police official, Muhammad Masood Khan Afridi, confirmed the attack and casualties.