Keane, 43, was at Manchester Magistrates’ Court accused of behaving aggressively towards cab driver Fateh Kerar, 44, near traffic lights in Ashley Road, Altrincham, on January 30.
The Irishman denied the Section 4A Public Order offence, giving evidence from the witness box himself and after a half day trial, was found not guilty.
District Judge Duncan Birrell said there was something of the “thwarted fan” about Mr Kerar and Keane’s lawyer described the whole incident as a “storm in a tea cup”.
The court heard that the footballer followed Mr Kerar to a set of traffic lights.
Mr Kerar told the court: “He was very aggressive. He was swearing at me. It was very bad. I responded and said ‘get back in your car’ and he went back to his car.
“I was shaking. I didn’t expect it. He was very aggressive.”
Keane told the court he did not flick a ‘V’ sign at Mr Kerar after the football fan told the court “I love Roy Keane”, but claimed the Old Trafford legend gave him “bad looks”.
Mr Kerar said Keane later followed him in his car before flicking the ‘V’ sign then getting out of his black Land Rover and approaching the cab swearing at him.
Keane said he was “chilling out, relaxing” in his car waiting for his wife when he noticed Mr Kerar across the road in his taxi.
Keane said they nodded to acknowledge each other but as they both moved off in their cars the cabbie made a gesture.
Pushing the corners of his mouth up with his fingers, Keane told the court: “He gave me a smirking gesture.”
The former player, now of Hale, Cheshire, was then cleared of causing harassment, alarm or distress to Mr Kerar.
Keane enjoyed a trophy-laden playing career at United following his move from Nottingham Forest.
He finished his career at Celtic and went on to manage Sunderland and Ipswich Town before becoming assistant boss at Aston Villa.
Keane quit Villa Park earlier this year to concentrate on a similar role he holds with Ireland’s national team.