Moussaoui's current lawyers contend his 2005 guilty plea was invalid because his trial attorneys could not tell him about classified evidence prosecutors knew about that could have aided his defense, the Richmond Times-Dispatch reported.
But government attorneys argued Moussaoui, now serving life in prison for his role in plotting the deadly attacks, entered his guilty plea in federal court in Alexandria over his attorneys' objections.
It's not known when the three-judge panel of the 4th U.S. Circuit Court of Appeals will issue a ruling.
So while his lawyers say he was unable to make a "counseled" decision, prosecutors counter he knew "the gist" of the evidence against him, the Times-Dispatch said.
Part of Monday's hearing was closed because classified matters were discussed.