"The man was arrested on suspicion of threatening behaviour and is currently in custody at a west London police station. No reports of any persons injured and no firearms were deployed," the spokesman said, as quoted by the Mirror newspaper on Sunday.
According to the newspaper, the London police were called to the Terminal 3 at Heathrow Airport at about 7:00 GMT after receiving a message about a man armed with a knife.
The police said that the detained man is in his 20s.
It was noted that the object he was carrying was not a knife, but another metal object.
Last November, armed police responded to a suspicious package in Heathrow's Terminal 4, which resulted in a brief airport's lockdown, however, the item turned out to be harmless.