The Australian-born star, 87, is accused of groping the schoolgirl after he appeared in a broadcast of the BBC’s Saturday Superstore in 1983, jurors were told.
Prosecutor Jonathan Rees QC told the jury of seven women and five men Harris approached the girl in the green room after filming of the episode, which also featured Wham!, had ended.
The lawyer said: “She recalls him sliding his open right hand across her back over her clothes and touching her breast.
“He then said ‘do you often get molested on a Saturday morning?’ which the prosecution suggests clearly shows the sexual nature of the touching.”
The Animal Hospital host is standing trial accused of indecently assaulting three teenage girls in the 1970s and 1980s.
He is also alleged to have indecently touched a 14-year-old girl in 1971 after she asked him for an autograph at a music event for children in London.
The musician and artist is also accused of twice groping a third teenage girl after being paid £100 to appear on ITV celebrity show Star Games in 1978, and telling her she was “a little bit irresistible”, the court heard.
Mr Rees added: “In essence the prosecution alleges that for his own gratification Harris groped these three young females in a sexual way, without their consent.”
Harris appeared via videolink for his trial at Southwark Crown Court in London.
He denies four charges of indecent assault against three women between 1971 and 1983.
Mr Rees told the jury: “The prosecution suggests that it offends common sense to suggest that these three women, independent of each other, should choose to fabricate stories of a similar nature.
“We say Harris had an appetite for touching young females.”
Harris, dressed in a grey suit, with a white shirt and a dark blue tie, listened with his arms folded as the woman who was 14 in 1971 gave evidence.
She told the jury when she approached him for an autograph at the event attended by hundreds of under 18s and their families at the Lyceum Theatre he used both hands to pull her onto his lap.
Giving evidence via videolink she said: “He pulled me onto his knee.
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“I stood up and he put his hand up my dress.”
She added his hand went “between her legs”.
When Mr Rees asked how that had made her feel, she replied: “Terrible.”
She said after it happened she went and told her father Harris had put his hand “somewhere private”.
Her father, who has since died, went and spoke to Harris, she said.
But she added she did not mention the alleged incident to her mother for many years afterwards.
Mr Rees asked what she did in later years if she saw Harris on television.
She replied: “I didn’t want to see him on TV. I would always turn the TV over.”
The trial is due to last for three weeks.