The plane was coming from Dallas-Fort Worth International Airport when an air marshal notified authorities of five men he considered suspicious, according to Marc LaVorgna, a spokesman for the Port Authority of New York and New Jersey.
CBS News correspondent Bob Orr reports that a stewardess became suspicious after she saw one or two out of a group of male Arab passengers reading flight manuals.
The plane landed in Newark without incident and was met by local law enforcement, Orr reports.
Port Authority police took the five men into custody immediately after the plane landed at 3:20 p.m., LaVorgna said.
They had no weapons, said Tim Smith, an airline spokesman.
The five men, who were later identified as four Angolan military personnel and an Israeli, were held for about three hours at the airport Saturday evening.
They were let go after authorities determined they were simply returning to their home countries after attending a U.S. helicopter training school.
The plane was carrying 121 passengers and five crew members. All other passengers were released soon after the plane landed.