The Norway-based private group, "Fedrelandet viktigst" or "Fatherland first", engaged in heated debate over the mix-up, the Washington Post reported.
The image, showing six empty seats on a bus, was posted and shared with the group's almost 13,000 members by journalist Johan Slattavik, who captioned it, "What do you think of this?"
The post sparked a strong response from members who posted comments such as, "disgusting", "frightening" and "tragic".
One user even said, "It looks really scary, should be banned. You can never know who is under there. Could be terrorists with weapons."
Slattavik told local news organisations that it was a little practical joke and he wanted to see how people would react.
"I laid out the photo to see what happened," he said, adding that he was shocked so many people fell for it.
Sindre Beyer, a former politician, noticed the mistake and shared the post on his account.
