The video from the group calling itself Swords of Truth showed four men sitting on the ground. The name of Norman Kember, could be read on a British passport shown in the video.
The Briton was among four aid workers - including two Canadians and an American - who were snatched in Baghdad on Saturday.
Al Jazeera did not say if the tape included a threat against the men's lives. It said the group accused the men of being "spies working for the occupying forces" while working for a Christian group.
The four hostages were working for peace and humanitarian group Christian Peacemaker Teams, one of the few remaining aid groups operating in Iraq.