Photos published on an ISIL website showed that they were brutally killed by daggers and pistols, Shafaqna website reported.
The terrorists had accused the six men belonging to Iraqi popular forces of Irtidad (apostasy).
Iraq has been facing the growing threat of terrorism, mainly posed by the ISIL terrorist group, which is believed to be supported by the West and some regional Arab countries.
The ISIL militants made swift advances in much of northern and western Iraq over the last summer, after capturing large swaths of northern Syria.
They have been committing heinous crimes in the areas they have taken, including the mass execution of civilians.