Tarik Shah, who also is a jazz musician, entered his plea before a federal magistrate in U.S. District Court in Manhattan. Shah, 44, faces up to 15 years in prison at a sentencing scheduled for July 10.
He became the third of four defendants and the second this week to plead guilty in the case, which also involves a Washington, D.C., cab driver, a Florida doctor and a New York bookstore owner. The doctor, Rafiq Abdus Sabir, has not pleaded guilty.
Shah admitted that he and others conspired from October 2003 through May 2005 to provide material support to al Qaeda.
He admitted to a conspiracy charge that accused him of agreeing to provide martial arts training to fighters while knowing al Qaeda was engaged in terrorism.
"I agreed with others to provide material support to al Qaeda in the form of martial arts training, which I knew was wrong," Shah said.
A prosecutor asked Shah to say he knew al Qaeda was a terrorist organization, but Shah, after a pause of several minutes to consult with his lawyer, agreed only that he knew the U.S. secretary of state had designated al Qaeda as a terrorist organization.
Court documents in the case alleged that Shah met in 2005 with an undercover FBI agent he thought was an al Qaeda recruiter.
During the meeting, he pledged allegiance to Osama bin Laden and al Qaeda and agreed to provide martial arts expertise to al Qaeda fighters, according to the documents.
Prosecutors also said Shah met multiple times from 2003 through May 2005 with a confidential source and an FBI undercover agent, expressing a desire and intention to help al Qaeda by recruiting others.
Shah also was accused of looking for locations where training could be conducted, the government said. He described an attempt to enter Afghanistan in 1998 to attend terrorist training camps there, it said.
Among materials recovered from Shah were names and telephone numbers of other people, including Seifullah Chapman, a member of what the government called a "Virginia jihad network" that prepared to join the Taliban by playing paintball in Virginia in 2000 and 2001. Chapman was convicted in 2004 and sentenced to 65 years in prison.
On Monday, cab driver Mahmud Faruq Brent Al Mutazzim pleaded guilty to providing material support to the Lashkar-e-Taiba organization, which the United States designated as a terrorist organization in 2001.
Bookstore owner Abdulrahman Farhane pleaded guilty in November and was scheduled to be sentenced next week.
Sabir is scheduled to go to trial on April 24. He was charged after prosecutors said he agreed to treat holy warriors in Saudi Arabia.
Sabir has argued it is unconstitutional to prosecute a doctor for providing medical services.
U.S. District Judge Loretta A. Preska has ruled the case can go to trial, saying "any reasonable doctor" would know that pledging to provide medical support to wounded terrorists under the control and direction of al Qaeda would be a form of outlawed "expert advice or assistance."