At the Special Criminal Court in Dublin on Tuesday, Patrick Mc Daid said that Sgt Niall Coady stopped him in a car with his three co-accused in the border village on March 16 last.
He told his counsel Mr Brian McCartney QC that he asked him his name and then asked the names of three other men.
"He said turn the ignition off. He reached in and took the keys of the ignition," he added.
The court has heard that the four men were arrested the day after a Real IRA press conference was filmed by the BBC in Derry. A Detective Garda has identified two of the accused, Gary Donnelly (38), of Kildrum Gardens, and Martin O'Neill, (40) of Colmcille Court, as men photographed in the background of the press conference given by three masked men. Michael Gallagher (28), Sackville Court, and Patrick John McDaid (38), Marlborough Street, are also on trial.
All four have pleaded not guilty to membership of an unlawful organisation styling itself the Irish Republican Army, otherwise Oglaigh na hEireann (IRA).
McDaid told his counsel he was driving to Bridgend to get some diesel and have "a quiet pint" in the 19th Hole bar. He said that, after taking his keys, Sgt Coady moved to the back of the car and was talking on his mobile phone. He said he got out of the car and rang his solicitor, Mr Paddy MacDermott.
He said the four men were standing outside the car at the side of the road for about 30 minutes and at one stage he said to Sgt Coady that he was going to get cigarettes from a nearby garage to which Sgt Coady replied: "No, you are not."
McDaid said that a large number of gardai then arrived in a convoy and Sgt Coady arrested him and he was taken first to Burnfoot Garda Station and then to Letterkenny. He said that the Sergeant did not explain to him why he was arresting him.
Defence counsel for the four men have submitted that their detention by Sgt Coady was not lawful and the court was due to rule on that issue.