The pilots of the Boeing 777 requested to land at Moi International Airport in Mombasa after the package was discovered in the toilet.
The aircraft was safely evacuated and the item is now being examined by bomb experts, police spokesman Charles Owino said.
The airport was also evacuated.
Flights have now resumed, Kenya’s airport authority said on Twitter.
The plane was carrying 459 passengers and 14 crew members and had left Mauritius at 01:00 GMT, Mr Owino said.
It had been due to fly directly to Charles de Gaulle airport in Paris.
One of those on board, Benoit Lucchini, said passengers were calm and were told by the crew that the plane was being diverted because of a technical problem.
“The plane just went down, slowly, slowly, slowly, so we just realised probably, something was wrong,” he said.
“But the personnel of Air France were just great, just wonderful. So they keep everybody calm and really quiet.”