The 31 year old showed no emotion as Judge Neil Rafferty QC imposed "nine months immediate custody" for the June 2018 offence.
From Crawfordsburn Road in Newtownards, Anderson was jailed for committing an act of a lewd, obscene and disgusting nature outraging public decency.
The sentence marks the second Crown Court conviction for Anderson, who was given a three-year suspended sentence last July after he admitted secretly recording 11 women over a period spanning 2005 to 2013.
As he sent Anderson to prison for exposing himself and performing a sex act in his mother's BMW sports car in view of the schoolgirl, Judge Rafferty said: "The time has long since passed when women and girls going about their business in public should be confronted by men like Mr Anderson."
Despite his protests of innocence, Anderson was convicted by a jury at Belfast Crown Court in October for the offence, which occurred on St Jude's Parade on the afternoon of June 20, 2018.
The schoolgirl who witnessed Anderson's behaviour - who was 12 at the time and who is now 16 - said the incident made her feel "worried and uncomfortable."
Anderson found fame on TV talent shows The Voice and Andrew Lloyd Webber's Superstar, and gained the nicknamed 'Baby Jesus' while touring as an understudy in the UK production of Jesus Christ Superstar.
When he gave evidence at the trial, Anderson said the girl had made a “genuine mistake” and that he was not carrying out a sex act and was only strumming his miniature guitar.
In a statement she made regarding what happened, the teenager said the incident has affected her confidence and mental health.
She also said in her statement, “because Jeffrey didn't plead guilty it made me feel as if I was lying and also going to court has been stressful”.
Judge Rafferty paid tribute to her and said: "She is clearly an intelligent and determined young woman. I can entirely understand the pride that her parents have in her and how she has conducted herself.
"Having noted how this prosecution has lingered over her for the last four years, now that it's concluded I can only encourage her to focus on becoming the author of her own life story - a story in which Jeffrey Anderson becomes relegated to a mere footnote."
Despite the jury's decision, Anderson continues to deny the offence and maintains he was playing his guitar with a bobble wrapped round the top of his thumb which made it red.
The judge said that after reading a pre-sentence report, it was clear Anderson had a "happy and stable upbringing where he had many advantages in life."
He added it was also apparent Anderson "seeks to explain and in some way justify his previous convictions due to a medical condition he endured as a teenager."
Judge Rafferty said that while he accepted Anderson has not offended since June 2018, that offence was committed whilst he was on bail and under investigation for the voyeurism charges.
Citing the fact the crime was committed close to three schools as a aggravating factor, the judge also highlighted the young age of the schoolgirl at the time and the impact the incident has had on her.
She sat in the public gallery with her father and watched Anderson being placed into handcuffs and led from the dock and into custody by prison staff.
As well as being jailed, Anderson was placed on the Sex Offenders Register for ten years and had been banned from working with children and vulnerable adults.