"We are apparently dealing with an individual suicide, which is under full investigation," OU President David Boren said in a statement.
There were no other reports of injuries. There was no word on the identity or sex of the person who died.
The loud noise of the explosion could be heard clearly inside Oklahoma Memorial Stadium, where 84,000 people were watching the Oklahoma Sooners play Kansas State.
Officers cordoned off an area west of the stadium, known as the South Oval, and nobody was allowed out of the stadium immediately after the blast, which occurred shortly before 8 p.m. People were allowed out of the stadium about 8:30 p.m.
A police bomb squad detonated explosives found at the site of the blast. The detonation could also be heard in the stadium area. The area near the stadium was searched by bomb dogs.
"At no time was anyone in the stadium in danger," Boren said.
Kerry Pettingill, Oklahoma homeland security director, said the incident was under criminal investigation and the motive behind the explosion was not known.
As fans streamed out of the stadium after the game, they were routed around the crime scene. Some fans leaving the stadium were escorted by police to buses that were parked near where the explosion occurred.
The state Medical Examiner's Office was on the scene as was the Norman Police Department, firefighters, the FBI and officials of the Bureau of Alcohol, Tobacco, Firearms and Explosives.
FBI spokesman Gary Johnson said an FBI bomb technician was providing assistance to local police. Emergency vehicles, including fire trucks, surrounded the area.
OU police Sgt. Gary Robinson said the body had not been removed as of late Saturday night as a bomb team continued to check the area for possible explosives before detectives could move in for their investigation.
Jaclyn Hull, an OU freshman, said she was leaving the game shortly before the explosion.
"We saw a little bit of smoke, about as much as you would see coming up from a grill," she said.
Stan Hilton of Tulsa said he heard the explosion while he was watching the game from his seat near the field.
"I became afraid at halftime when they had us locked in the stadium," he said after he left the stadium.
Larry Lucas II, an OU senior, said at the time of the explosion he was in the university's architecture building near where the blast occurred.
"At first I thought it was a prank because that's where the Kansas State buses were parked," he said. Lucas said he saw Kansas State players leave the bus before the game.
Authorities could be seen searching Kansas State players and coaches amid tight security as they boarded buses to leave the area.