An investigation into the theft has been started by the transport police following the incident at the city's Gare du Nord railway station a statement from the Paris prosecutor's office said.
The Paris Olympics will be held from July 26-Aug 11, with some 30,000 members of the police force expected to be mobilised every day.
About 300,000 spectators expected to attend the opening ceremony along the River Seine.
"Although he was careful to point out that his bag contained a professional USB memory stick ... it is important to specify that this stick only contained notes relating to traffic in Paris during the Olympic Games, and not on sensitive security plans," the prosecutor's office said.
"Initial checks revealed that the agent was not in possession of any information relating to the organisation and deployment of the police force during the Olympic and Paralympic Games," Paris City Hall said in a statement.
"This computer equipment contained notes for internal use, relating to his work in the IT department of the Highways and Transport Directorate. All the necessary resets were carried out in order to cut off all access to the City's IT system."
The City said sanctions could be taken.
Paris 2024 organisers declined to comment.
-Reuters