According to initial reports, the militants had planted the IED on the road, near Tehsil Mahmund Bajaur Agency.
When the device exploded, it killed three civilians and injured three others.
Last week, a blast outside a mosque killed two men and injured three in the Kacha Pakka area in Kohat.
The explosives were fitted to a motorbike, said DSP Mushtaq Hussain.
Unidentified militants had detonated the bomb with a remote control as soon as the people stepped out of the mosque.
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