An American Airlines flight bound for New York City was stopped before takeoff at San Francisco International Airport after there was a threat to the plane.
Passengers were removed from the flight, taken by bus to a terminal, and sent through security a second time.
Two individuals on the plane were taken into custody, according to one witness.
American Airlines Flight 24, bound for New York City, was scheduled to take off at 0730 local time (1430 GMT).
But the Boeing 767, which had 163 passengers and 11 crew members on board, was grounded at approximately 1000 after a late departure from the gate.
Uniformed police handcuffed a young man and woman sitting in the back row of the flight and removed them from the plane, passenger Michael Kidd told the Associated Press news agency.
The FBI said at least two people were being questioned about the incident.
It was unclear whether a bomb or hijack threat prevented the flight from leaving the airport, as federal authorities gave mixed information about the incident on Thursday.
Passengers sat for an additional two hours on a remote area of the tarmac after the already delayed flight was ordered to stay grounded.
Mr Kidd said there was "no fear in the cabin" as passengers on the flight awaited instructions.
"Even with the frustration of having to sit there, there were no raised voices," he said.
Some of the passengers on the plane used their laptops to search the internet for information about the incident.