A Tasmanian man who set up a video camera to capture paranormal activity in his house ended up accidently recording his partner of 11 years cheating on him - with his own teenaged son.

After setting up the camera, the man forgot to switch it off during the day. When he returned from work the next day, he discovered his partner kissing and cuddling with his 16-year-old son in the recorded video footage, themercury.com reported.

Soon after discovering what was going on in his house, the man decided to call the police.

When asked about the incident, the 28-year-old woman initially denied intercourse with the teenager. However, in a subsequent interview recorded by police, she admitted to having sex with him twice.

The man's son, who is a year below the legal age of consent in Tasmania, admitted to having sex with the woman three times.

In her defence, the woman said that although she was aware of the boy's age, she thought the age of consent was 16. However she later pleaded guilty to having sex with a minor.

Crown Prosecutor Jackie Hartnett told the court that in October last year, the woman had gone to the boy's room to discuss his driving lessons. However despite a strained relationship between the two, the conversation that night led to kissing and ultimately to intercourse.

The court also heard that after the incident in October, the woman followed the teenager to another part of the state where they had sex several times in a hotel room.

Although the woman has a child with the man, they have separated following the affair.

"She accepts this is not a relationship which can or will continue," defence lawyer Steve Chopping told the court.

At present, the woman is remanded in custody and awaits her sentence on Monday.