Air France had filed a complaint against the passenger for reckless endangerment and obstruction to the circulation of an aircraft, the Bobigny district prosecutor's office told CNN in a statement.
The passenger was a former French policeman who retired eight years ago and was living on the island of Reunion, a French territory southwest of Mauritius in the Indian Ocean, a spokesman for the French National Police told CNN.
The man claimed he found the suspicious device on board the aircraft, forcing Flight 463 to divert to the Kenyan coastal city of Mombasa early Sunday, but his story didn't add up, the spokesman added.
The passenger was taken into custody at Paris Charles de Gaulle Airport, the original destination of the flight from Mauritius before it was diverted to Kenya.
The object was analyzed and found to contain no explosives, the airline said.
Air France CEO Frederic Gagey described the object at a news conference Sunday as a cardboard box containing papers, with "something like a kitchen timer" inside it.
It was found by a passenger in a cabinet behind the restroom mirror, he said. He could not say whether the object was assembled before the flight, but the materials would not usually be on board the aircraft.
Joseph Nkaissery, Kenya's interior minister, told CNN on Sunday that Kenyan authorities questioned four passengers from the flight over the incident. Those four were later released and allowed to travel on to Paris with the other passengers, Mombasa County Commissioner Nelson Marwa said Monday.
'It seems like a nasty joke'
Gagey said an inquiry will determine who planted the item in the restroom, an act he described as "stupid" and "completely unacceptable."
"It seems like a nasty joke," he said. "This is behavior which is in extremely bad taste."
The 473 stranded passengers and crew were evacuated from the aircraft by slides and accommodated at a hotel in Mombasa before being returned to France, he said.
There had been no security failure by Mauritian airport authorities, because the item contained no explosives and was not something that would be picked up in screening.
Nevertheless, the airline said it was reinforcing security measures in Mauritius.
Airport shut down
The airport was temporarily shut down following the incident, but has since reopened, according to the Kenya Airports Authority.
The island nation of Mauritius sits in the turquoise waters of the Indian Ocean and is a popular tourist destination known for its pristine beaches.
Mombasa, which is along the Indian Ocean, is the second-largest city in Kenya.