Preston Wiginton was turned back at Heathrow when he arrived for the party's Red, White and Blue festival in Codnor, Derbyshire, which started today.
A spokesman for the UK Border Agency said Wiginton was sent back to New York because it was believed his presence in the UK could stir up racial tension. He said he could not confirm reports that Wiginton, who has links with the BNP leader, Nick Griffin, was due to speak at the festival.
A Home Office spokesman said: "The government opposes extremism in all its forms and we will prevent those who want to spread extremism, hatred and violent messages in our communities from coming to our country."
The BNP today denied reports that Wiginton was due to speak at the festival. Simon Darby, the party's deputy leader, said: "I know Preston, he is an American chap. He came to last year's Red, White and Blue and was coming to this year's but they wouldn't let him in for some reason. He wasn't coming to speak."
The festival runs until tomorrowSunday. Last year's event sparked violent scenes, with 30 anti-BNP protesters arrested. A high-profile policing operation has been put in place by Derbyshire police for this year's rally amid fears of more clashes.
Unite Against Fascism plans to protest against the festival today and tomorrow, with supporters coming from across the country to take part in an organised march.
UAF published an open letter on its website condemning the event, saying BNP claims that it was a "patriotic family festival" were untrue and that last year's guests included a Czech neo-Nazi and a Swedish fascist.