The judge in the case directed the jury to clear the actor of the charge after the prosecution offered no further evidence.
Roache remains on trial over two counts of rape and four counts of indecent assault involving five complainants who were aged 16 and under.
The alleged incidents are said to have happened on dates between 1965 and 1971.
The actor, who plays Ken Barlow in the long-running soap, denies all the charges.
He was cleared of the indecent assault charge at Preston Crown Court on Monday.
The allegation was one of two made by a woman who said she was aged 14 when Roache twice made her perform a sexual act on him.
Giving evidence, the complainant said the actor first struck in the gents' toilets at Granada Studios in Manchester in the summer of 1965.
Jurors were then shown a letter and signed photograph that Roache, 81, had sent to her after that alleged incident in which he asked to her write back to him when she returned to school.
The woman claimed later that same year she was picked up by the actor from the studios in his Rolls-Royce and they had a conversation of a sexual nature.
She said she thought that she had also been indecently assaulted in his car but she had ''no actual memory'' of the episode.
The judge in the case, Mr Justice Holroyde, said: "In relation to that episode the witness was not giving evidence that it did happen, she was giving evidence that she was thinking it did happen and that is not a sufficient evidential basis for the conviction of an offence."