The man allegedly failed to register as a 'foreign agent' under a Russian law that carries several years' jail time for offenders.
Russian authorities say they have arrested a French national on suspicion of espionage offences.
As reported by state-owned news agency TASS, the Russian Investigative Committee says it has launched a criminal case against the unnamed man, who allegedly "failed to register himself as a foreign agent in compliance with Russian legislation" and "has been gathering information on Russia's military and military-technical activities".
"This information, when obtained by foreign sources, can be used against the security of the state," the committee said in a statement. "For these purposes, he repeatedly visited the territory of Russia, including the city of Moscow, where he held meetings with citizens of the Russian Federation."
If convicted, he faces a sentence of up to five years' imprisonment.
Investigators have released video purporting to show the unidentified man at a Moscow restaurant.
A number of westerners have been arrested by Russian authorities in recent years, in some cases resulting in serious diplomatic tensions and public outcry.
Among those still in custody is Wall Street Journal reporter Evan Gershkovich, who was arrested in spring 2023 for supposedly conducting espionage on behalf of the US government.