Hassan Adan, an elder in Qandala town in the semiautonomous state of Puntland, says the bodies found along a road near the town showed signs of torture.
Puntland officials were not immediately available for comment.
Heavily armed fighters on Saturday stopped a truck carrying nearly two dozen passengers about 25 kilometers (15 miles) from Qandala and abducted nine people.
The abducted included off-duty soldiers returning from areas where troops are battling the IS-linked fighters who had briefly captured Qandala.
It was not immediately clear if the decapitated bodies were those of soldiers.