The FBI says the arrests were part of "an ongoing investigation." The charges were not immediately detailed.
Medunjanin's attorney says the FBI seized his client's passport on Thursday. Robert C. Gottlieb says he was not officially notified that his client had been arrested after being treated for minor injuries from a traffic accident.
Gottlieb says the search warrant indicates the passport was sought as part of an investigation into a conspiracy to use weapons of mass destruction.
Najibullah Zazi has previously pleaded not guilty to that charge.
The Colorado airport driver is accused of getting al-Qaida training to build homemade bombs to attack New York City.