The 12-minute video released on social media on Wednesday mimics a participatory television show, in which members of the public are interviewed and invited to take part.
Produced by the group's branch in Nineveh province, of which Mosul is the capital, the video starts with footage of destruction it presents as the result of US-led air strikes against it.
It also shows the bodies of dead children.
The video moves on to the ‘confessions’ of five men from Mosul, detailing how they passed on intelligence on the activities and positions of the jihadists in Nineveh, most of which is still controlled by IS.
Five IS executioners are then shown standing behind the five accused in orange jumpsuits, holding knives.
One fighter turns to the crowd: ‘O Muslims, who amongst you wants to get closer to God through these disbelieving apostates?’
Hands go up, he picks ‘volunteers’ and the five IS fighters in combat gear are replaced by ‘civilians’ to whom they give their handguns to shoot the accused in the back of the head.
Residents are subsequently interviewed about the group execution, with one saying he wished he had been selected to take part.
The video was released the same day IS claimed responsibility for three Baghdad bombings that killed at least 94 people, the deadliest spate of attacks to hit the Iraqi capital this year.
Most of the victims of the attacks were civilians and included many women and children.
