Kennedy, D-Mass., who has been battling brain cancer, was removed from the Capitol by stretcher with Sens. Orrin Hatch, R-Utah, John Kerry, D-Mass., and Christopher Dodd, D-Conn., by his side and whisked to Washington Hospital Center. Hatch said by the time they reached the ambulance, Kennedy seemed to be returning to normal.
Doctors said tests indicated the seizure was brought on by fatigue and Kennedy would be released Wednesday morning, a statement issued by Kennedy's office said.
"He seemed to be going into a kind of seizure," former Vice President Walter Mondale told ABC. "I'm told he's doing much better now. He seemed to be in great difficulty for a brief period."
Mondale, who sat at the table with Kennedy, and Kerry and their wives, said they had been chatting for about 20 minutes "telling old war stories" before the seizures began.
"He was keeping us all laughing," Mondale said.
The Hill quoted witnesses as saying Kennedy's eyes rolled back in his head, his teeth clenched and his hands shook. The incident lasted about two minutes. He was removed from the room by medical personnel to the Rayburn Reception Room.
The incident came before Congress presented Obama and Vice President Joe Biden crystal bowls and photographs of the inauguration commemorating their ascension to office.
In his remarks after the presentation, Obama called Kennedy a "warrior for justice" and said he would be in his prayers.
"I would be lying to you if I did not say that right now a part of me is with him," Obama said.
A moment of silence was also held.
ABC News reported Sen. Robert Byrd, D-W.Va., the oldest member of the Senate, was so upset he was removed from the luncheon in a wheelchair.