A priest has received a suspended sentence for the 2015 sexual assault of a teenage boy after a court heard he has been put under effective house arrest by his order.

Dublin Circuit Criminal Court heard the 65-year-old, who cannot be named for legal reasons, molested the boy, who was in his early teens, after mass one Sunday in September 2015.

The victim told his mother about the incident the following month and she went to gardaí. The accused was interviewed and said he accepted the boy's allegations and apologised.

A garda told the court that the priest had been since living under strict rules in a different house operated by his order. The order also cannot be identified.

He is not allowed celebrate mass or wear "priestly garb" and is not allowed leave the house alone except to go to his doctor or solicitor, the court was told.

He is also not allowed unsupervised access to children or vulnerable adults, including his own family. The regime is to continue "indefinitely", Ronan Kennedy BL, defending, told the court.

Judge Melanie Greally said the man's current situation "has correctly been compared to house arrest" and that she was taking this into account in sentencing.

She also considered the man's early guilty plea, his remorse and his "good work" in missions around the world.

She imposed a two year sentence which she suspended in full on condition the priest completes a sex offenders programme. He has already been registered as a sex offender.

The man pleaded guilty to one count of sexual assault of the boy in a church building in Dublin in September 2015.

A local garda told prosecuting counsel Cathleen Noctor BL that the boy's family regularly attended the church for mass. Afterwards, the adults would have tea in a kitchen while the children would hang out in another room because it had internet access.

One Sunday after mass the boy was in the room using the internet when the accused entered. He molested the boy by putting his hand down the child's trousers. He also took the boy's hand and put it down his trousers. The incident lasted about 15 seconds.

As the priest was leaving the room he told the boy: "Don't think I'm bad alright. I'll see you later."

The following Sunday he saw the boy and asked him: "Are you alright, are you shaken up or anything?"

The child declined to write out a victim impact statement although the garda said he continued to be "very upset" by the incident. The boy's parents had not told him until two weeks ago that the matter was before the court.

Mr Kennedy said the matter was originally before the District Court but was sent forward to the Circuit Court by a judge at the last minute because it was judged to be too serious.

Counsel said his client was genuinely remorseful and had no previous convictions. He said the offence was "heinous" but did not involve threats and lasted a short time.

He added that the priest has been undergoing sex offender therapy since last year.