She was taken into custody at her house by security agents on Sunday, according to the website, which is linked to opposition leader Mir Hossein Mousavi.
Mohammadi directed the film "Women Without Shadow," and she contributed to a documentary by filmmaker Rakhsan Bani-Etemad about Iran's disputed presidential election in 2009.
Mohammadi's passport was confiscated to keep her from attending the Cannes film festive in May.
Speaking on the sidelines of a press event in Paris, Greek filmmaker Costa-Gavras said Monday he is worried about Mohammadi following her reported arrest.
