Dr. Rafiq Abdus Sabir, 52, was convicted in Manhattan federal court after a trial that featured testimony by an FBI agent who posed as an al Qaeda recruiter in a sting operation that led to four arrests.
The charges against the New York City-born Sabir carried a potential maximum sentence of 30 years in prison.
When the verdict was read, Sabir looked straight ahead. As he was escorted from the courtroom, he waved to supporters, who said, "Stay strong."
"We are deeply disappointed in the verdict," his lawyer, Ed Wilford, said.
Jurors had heard audio tapes of a May 2005 ceremony in a New York apartment in which Sabir and his best friend, Tariq Shah, a martial arts expert and jazz musician, pledged loyalty to al Qaeda and, the government alleged, Osama bin Laden.
Shah pleaded guilty just before trial to providing material support to a terrorist organization and agreed to serve 15 years in prison, though he has not yet been formally sentenced. A New York bookstore owner who pleaded guilty was sentenced to 13 years in prison. A Washington, D.C., cab driver has pleaded guilty and agreed to serve 15 years in prison.
Sabir had testified that Shah never told him he was talking with an al Qaeda recruiter. At the pledge ceremony, Soufan mispronounced al Qaeda more than a dozen times, Sabir said.
He also said he did not know "sheik Osama" meant bin Laden.
Prosecutors had no immediate comment on the verdict.