Olof Bergren, head of the Gamle Oslo library, has been campaigning for the prayer right to be granted in Oslo which has a population of about 500,000, including 36,000 Muslims.
Six months ago the World Islamic Mission applied to the city's authorities to allow a mosque in the old town - Gamle Oslo - to call the faithful to prayer through loudspeakers.
And at the same time the Norwegian Heathen Society - which claims there is no God - was also granted the right to broadcast its calls from a rooftop once a week, including the call: "God does not exist."
Heathen Society secretary, Harald Fagerhus, said that one's religion was a personal matter, but that "since the church bells and the preaching from the mosques have taken over the public space, we want to be able to do the same".
Until now, the only legal prayer calls in Norway, where Lutheran Protestantism is the state religion, have been the ringing of church bells.
Olof Bergren, head of the Gamle Oslo library, has been campaigning for the prayer right to be granted in Oslo which has a population of about 500,000, including 36,000 Muslims.
He said: "We have clocks on every church here and they are much more disturbing.
"The call for prayer is supposed to be only on Fridays at noon, whereas you hear the church bells every day and night."
Mari Linlokken, deputy director of the Anti-Rasism Centre in Oslo, said the decision was of great symbolic importance.
"All over Norway you have churches and their bells are tolling every Sunday and by giving permission to this mosque, I hope that other mosques in Norway will be able to call to prayer too."
Jan Willy Lang, a Labour member of Oslo council, said the atheists would not cause too much trouble for the Muslims.
"To give fair treatment we had to say "yes" to the atheists, but I don't think they will climb on the roof and shout too often."