The woman, who had been in Iran for five months, is reported by the AFP news agency to be an academic in Isfahan.
The woman had been detained by police at Tehran airport as she was getting ready to leave for Beirut.
The French foreign ministry said that the ambassador for Iran in France had been summoned to explain the matter.
Relationships between Iran and France and the UK have been deteriorating recently since the Iranian presidential election was disputed last month.
The supreme leader of Iran, Ayatollah Ali Khamenei, is reported to have issued a warning to Western countries, not to meddle in Iranian affairs.
