Tommy Hol Ellingsen, 28, and his girlfriend Leona Johansson, 21, say they did it to help save the rain forest.
Police fined the couple £850 each but are refusing to pay and now face a full court case, reports Aftenposten.
Ellingsen and Johansson are members of an organisation called F*** for Forest which is dedicated to having sex in public to save the environment.
Their latest stunt came in the middle of a concert by Kristopher Schau and his band Cumshots at the Quart music festival in Norway.
After the couple walked on stage, Ellingsen asked the audience: "How far are you willing to go to save the world?"
He and Johansson then took off their clothes and began their enthusiastic performance as the band carried on playing around them.
The couple previously raised about £10,000 by haviung sponsored sex in public but couldn't find an organisation prepared to take the money.
However, the conventional green movement is less than enamoured with their tactics.
"I can not see that this helps the work for the rainforest," said Lars Løvold, head of the Rainforest Foundation Norway."
