The two volunteers were on their way to administer polio drops to children in Mali Khel area of Kurram Agency when their motorcycle hit the bomb buried under the road.
They were killed instantly, officials of the local political administration said.
The bodies of the two men were taken to a hospital in Parachinar, the main town of Kurram Agency.
The region has been rocked by sectarian clashes between rival Shia and Sunni groups as well as attacks by the Pakistani Taliban.
On Tuesday, a policeman was killed when suspected militants targeted a polio vaccination team in Swabi district of Khyber-Pakhtunkhwa province.
On January 1, six women and a man working for a NGO involved in polio vaccinations were shot dead in Swabi district.
Last month, eight volunteers involved in a polio vaccination campaign were gunned down in a string of attacks in the southern port city of Karachi and Khyber-Pakhtunkhwa province.
The attacks prompted UN agencies to withdraw their workers from the vaccination campaign.
Islamabad: Two members of a polio vaccination team were killed when their motorcycle hit a bomb in the restive Kurram tribal region of Pakistan on Thursday, the latest in a string of attacks targeting volunteers engaged in a drive against the crippling disease.
First Published: Thursday, January 31, 2013, 13:49