At around 1:35 p.m. Houston police say they were called to a "discharge of firearm" at Terminal B. Police say the suspect discharged his weapon into ceiling one time. That's when a Department of Homeland Security agent told him to drop his weapon.
The Houston Police Department says the suspect then turned toward the agent, who fired at the man at the same time the suspect shot himself.
Police say they could not yet determine the man's cause of death as to whether it was self-inflicted or not.
According to police, they are not looking for anyone else at the airport who may be involved in the shooting.
Witnesses tell ABC13 in Houston that they heard a couple of gunshots ring out and a TSA agent told everyone to get down.
Dale Howard, of Tomball, was at the baggage handling area of the airport waiting for his sister to arrive on an incoming flight when he heard two shots fired from the floor above. A few seconds later, he said he heard three more shots.
"People were screaming. I knew exactly what it was -- gunfire," Howard said.
Police from an adjacent station rushed in, and Howard said he directed them to the floor above.
Greg Newburn, who was in the terminal waiting for a flight to Oklahoma City, said he was sitting in a cafe area when he heard two gunshots and after a pause, several more.
"It seemed like quite a few shots. Everyone was scrambling, running left and running right, turning tables up and hiding behind tables. Nobody knew what was happening. I couldn't tell where the shots were coming from," he said.
Newburn, from Gainesville, Fla., said it took him a few seconds to realize that the shots had come from the terminal ticketing area, near the security checkpoint. Newburn said he didn't see who had fired the shots.
Terminal B has been shut down during the investigation and passengers are being sent to other terminals, according to the Houston Airport System.
The FAA has issued a ground stop for all flights at IAH.
Just last month, United Airlines unveiled the newly renovated Terminal B at IAH. The new 225,000 square foot South Concourse is four times larger than the previous facility and is used for United Express regional flights.
The terminal was expected to be fully operational as of yesterday.
The Associated Press contributed to this report.