She said Harris had said to her, "Do you often get molested on a Saturday morning?"
The woman's testimony came after the judge told the jury she had approved an application for bail allowing Harris to be released from Stafford Prison today.
Harris has been permitted to appeared by video-link from the jail for the first week of his trial on account of his age and state of health.
He is facing four indecent assault charges involving three women who accuse him of groping them when they were teenagers in 1971, 1978 and 1983.
Judge Deborah Taylor told the jury that her granting bail to Harris should have no impact on their decisions on the current charges.
She said the court would not be sitting on Friday as Harris went through his release from Stafford.
"He will be attending what remains of this trial in person from Monday next week," the judge said.
The court heard from the 1983 complainant that on New Year's Eve that year she was invited with her sister and other children to a live screening of an entertainment show at the BBC Television Centre featuring Harris.
She said that as a 13-year-old she was "a very big fan" of Harris and was excited she was going to meet him.
The woman said that after the screening the children were invited to a room where Harris came up beside her at a drinks table.
"I looked up and as I did he slid his right hand under my breast and said to me, 'Do you often get molested on a Saturday morning?'
"I was in shock because I couldn't comprehend really what had just happened. He left quite quickly and I just stood there for a while."
The woman told the court that she went across to her older sister and told her what happened but her sister just said something like, "That's Rolf Harris, don't be silly".
She said there was a similar response from her parents at home that night so she felt no one else would believe her and accordingly took her complaint no further.
But the woman said that in the intervening years she had told many people about what Harris did and every time he appeared on television she would call him a "pervert".
She said that after Harris was convicted at his first trial in 2014 she thought there was "a chance I might be vindicated", so she contacted police. The trial continues.
- AAP