Three of the people were rounded up from their homes for questioning early Wednesday, while the fourth was locked up later in the morning, according to media reports.
Militant members of the Ukrainian feminist group Femen were roughed up by several men when the women bared their breasts at a November 18th rally organized by the Civitas institute, a Catholic group against gay marriage.
Caroline Fourest, a journalist and essayist, was also attacked during the melee, which occurred on the sidelines of the demonstration, which attracted 9,000 people.
Fourest filed a complaint on November 19th which led to the Paris prosecutor’s office launching an investigation.
"Ten Femen activists had decided to make a peaceful and humorous protest, dressed as nuns with humorous slogans," Fourest was quoted as saying by Le Parisien newspaper.
"And when they are pushed toward the demonstrators, guys chased them, no holds barred," she said.
"The girls took hits in all parts of the body."
Civitas, for its part, has already launched a lawsuit against Femen members for “sexual exhibitionism” and protesting illegally, while offending a religious group by mocking their appearance.
The militants dressed up as bare-breasted nuns wearing only knickers and stockings.
They also threw tear gas canisters at the anti-gay marriage marchers, Civitas said.