A Tasmanian dad who was hoping to record some paranormal activity in his house got more than he bargained for. Instead of ghosts, he unwittingly videotaped his partner engaging in a sexual activity with his 16-year-old son.

The unnamed man hoped to capture evidence of paranormal activity in his home so he set up a camera. However, he forgot to turn it off, which led him to accidentally record another suspicious activity.

When he reviewed the footage, he was surprised to see his de facto partner kissing and cuddling his teenage son. When asked, the woman, 28, allegedly downplayed the incident, but his son admitted that they had sex three times, the Mercury reported.

The man called the police, and the woman finally confessed having sex with the boy twice. And although she knew his son's age, she claimed that she thought the age of consent was 16.

Crown Prosecutor Jackie Hartnett told the court that in October of last year, the woman went to the boy's room to discuss his driving lessons. They previously had a strained relationship, but their talk that day led to tickling and kissing, and then ultimately led to intercourse.

The woman, who has been in a relationship with her partner for 11 years, also followed his son in the following weeks to another part of the state to have sex with him several times in a hotel room.

She has a young child with the boy's father. The incident unsurprisingly had split the couple apart.

She remains in custody where she awaits her sentence on Monday.