The incident took place on a main thoroughfare in Peshawar, the capital of the northwestern Khyber Pakhtunkhwa province, which borders neighboring Afghanistan, Anadolu Agency reported.
Peshawar police chief Kashif Abbasi told reporters that the two suspected militants were transporting explosive material from one location to another on a motorcycle when it went off.
"Both militants were killed in the blast, while a passerby was critically injured," he added.
"It is confirmed now that it was not a suicide attack," he said.
Local broadcaster Geo News aired footage showing a charred motorcycle lying in the middle of the road, with security personnel cordoning off the site.