Ahmad Abousamra, 28, thought to be a US citizen now living in Syria, was also charged in 10-count indictment. Abousamra was named, but not charged, in October’s filing.
The suspects’ plans to carry out terror attacks were reportedly thwarted when they were unable to obtain automatic weapons.
Mehanna, trained as a pharmacist, lived with his parents in a leafy town in Boston’s suburbs.
He is in federal custody awaiting a probable cause hearing on Nov. 12. Mehanna was previously indicted in January 2009 for making false statements to the FBI in connection with a terrorism investigation.
Yesterday, the FBI released excerpts of blogs allegedly written by Mehanna on the appeal of martyrdom, and transcripts of phone conversations between Mehanna and Daniel Maldonado, a New Hampshire man now serving a 10-year sentence for getting al Qaeda military training.
In 2006, Mehanna reportedly helped translate into English an hour-long terrorist training video released by al Qaeda, entitled “Expedition of Umar Hadid.”