A clerk at a hotel in Alameda called the Alameda Police Dept. to report she had received an anonymous phone call making a threat against Flight 24.
The Transportation Security Administration requested the plane be moved to a remote location on the tarmac.
The FBI confirmed at least two people were questioned after San Francisco Police officers boarded the plane from the rear. It was reported the officers arrested the two people. A witness onboard said it was a young man and young woman who were arrested.
"No one was arrested. No one was placed in any handcuffs at this time that we know of," said San Francisco Police Sgt. Michael Rodriguez.
"[They] spoke to him a little bit, asked him to stand up, asked him if he had any belongings with him. He said yes, and they pointed to it and said 'Is this yours?' 'Yes.' They opened up another compartment and said 'Is this yours?' He said 'Yes,' and they picked it up and took it and then as soon as they turned around to exit the plane, they put him in handcuffs and the female traveler," said Michael Kidd, a passenger on the flight.
Other passengers were removed from the plane in groups and had themselves and their luggage re-screened for security.
"The pilot came on a couple times and eventually said there was a security threat that they thought was credible and that the SFPD was going to come over and take us off the plane, and eventually that's what they did," said passenger Jay Sears.
"People were pretty calm, considering the pilot made an initial announcement, and everyone sort of took it in stride. And then the second announcement about 20 minutes later was pretty intense -- that basically there is an issue and that we're going to be going back to the gate," said another passenger. "Just the tone of his voice sounded like, 'Gee, something's going on here.'"
The phone call reported a high-jack threat. An FBI official said the phone threat was later deemed non-credible.
The flight had 163 passengers and a crew of 11 onboard. The flight had already been delayed for two hours when the plane pulled away from the terminal and taxied to a remote section of tarmac, where passengers sat for another two hours.
The investigation was ongoing.
The Associated Press contributed to this report.