The Canadian Broadcasting Corp. reported an attempt by protesters to jump a fence and enter the main parliamentary building with dozens of police officers and security guards at the ready was a peaceful affair. The CBC said protesters and police were seen laughing and joking as the arrest took place.
Protest organizer Peter McHugh of Greenpeace called the demonstration "a historic mass act of civil disobedience."
The $7 billion Keystone XL pipeline is to ship crude oil from the province of Alberta to Texas.
"Participants are responding to a call to action for a large peaceful protest where many will risk arrest to tell the [Prime Minister Stephen] Harper government they don't support his reckless agenda," McHugh said in a release.
"Participants will also use this action to tell Harper we need to turn away from the tar sands and start building a green-energy economy that respects indigenous rights and prioritizes the health of the environment and communities."
Maude Barlow, head of the Council of Canadians, said environmental activists want to see the country move to alternate energy sources.
"Tar sands mining has destroyed much of Alberta's water table and will put the fragile Ogallala aquifer [the world's largest known aquifer] in peril," she said. "We join with the millions of Americans who oppose the expansion of this deadly industry."