Gary Trainor, who was on board the 8.20am flight, said some passengers began getting worried that the incident might be terror related.
After landing in Belfast, the actor and musician, who is currently performing in the West End, said: "I was in the middle of the plane and he was at the back so I wasn't really aware anything was wrong until I saw a police officer walk down the aisle.
"That is when lots of people started rubber necking to see what was happening. There was a black guy in his 40s and he seemed to be involved in a stand off with the policeman. He kept saying that he had paid for his ticket and therefore had every right to be on the aircraft.
"It seemed to go on for about 20 minutes and things became increasingly heated. More police officers came on board and then eventually there was a scuffle and I saw they had drawn their tasers.
"I didn't see them hit him but he slumped down and then it took about another 20 minutes to get him off the aircraft. There were whispers going round among the passengers that this might have been a diversion and people started to ask 'have they got all his luggage off'.
"There was a bit of panic among the passengers because he was being completely uncooperative. They eventually took us all off and checked the aircraft before letting us back on with another crew."
Mr Trainor said: "I was going home for a wedding and I was supposed to be out shopping with my mother so I was a bit concerned about the time. We were due to land at 9.40am and ended up touching down at 12.20pm instead, so it was a bit frustrating."
He has now been sectioned under the Mental Health Act.
A police spokesman said: "On Thursday evening, following examination by doctors, he was detained under Section 2 of the Mental Health Act for admission into a psychiatric unit for further assessment and treatment in the interest of his own health, safety and protection of others."
Easyjet said passengers had been taken off the plane as a security precaution.
Easyjet said in a statement: "EasyJet can confirm that police boarded flight EZY831 from London Gatwick to Belfast on August 20 due to a passenger behaving disruptively.
"Whilst such incidents are rare we take them very seriously, do not tolerate abusive or threatening behaviour onboard and always push for prosecution."