Judiciary spokesman Gholamhossein Esmaili did not identify the man, but said he "had been free on bail".
Iranian media reported last week that a US-Iranian businessman named Emad Shargi had been arrested has he tried to cross a western border illegally.
It could complicate plans by new US President Joe Biden to re-engage diplomatically with Iran.
His predecessor Donald Trump subjected the Tehran government to a "maximum pressure" campaign of crippling economic sanctions.