Lawless, a New Zealander, and six other protesters boarded the ship Noble Discoverer early Friday to prevent it sailing to the Arctic, where it has been contracted by Anglo-Dutch energy giant Shell to conduct exploratory drilling, AFP reported.
Five police officers had boarded the ship and made contact with Lawless and the protesters, while one man who was part of the protest was arrested on the docks, Fairfax NZ reported.
Lawless said her actions, which forced authorities to close the North Island port of Taranaki, were prompted by a desire to save one of the world's last pristine environments, AFP reported.
She was not concerned at the prospect of being arrested.
"That's the least of my concerns," she told AFP by cell phone from the ship. "I'm a true believer. We need to start switching over to renewable energy now, we don't have to go to the ends of the earth to suck out every last drop of oil."
Lawless, who starred as the title character in the fantasy television series "Xena: Warrior Princess" from 1995-2001, is a long-time environmental activist who was named as a Greenpeace ambassador in 2009.
Police said the protesters had climbed a drilling tower on the ship and were displaying banners.
"The protesters are clearly breaking the law by trespassing on the ship and we are currently liaising with the port of Taranaki and the harbor master to decide the most appropriate course of action," inspector Blair Telford said.