The man has been subdued by the US air marshals after he tried to cause some disturbance with his act.
"TSA (Transportation Security Administration) is monitoring an incident on board United Airlines flight 663 from DCA to DEN after receiving initial reports that a Federal Air Marshal responded to a passenger possibly causing a disturbance on board this aircraft," the agency said in a statement.
According to TSA spokeswoman Kristin Lee, the man is being questioned by the law enforcement in Denver.
Official said that t it was not clear as to what the man was upto unlike the Christmas eve terror scare.
They said that man could be trying to do something harmful like start a fire or explosion, or it could be something harmless like smoke of a cigarette.
Officials said that the man is a Qatari diplomat living in US for many years.
On Wednesday, Apr 7, officials said that it would be too early to term it as a terror threat as it could also be a gross misunderstanding.