In an appearance on the Late Show with David Letterman, which airs in the US tonight, Justin jokes about the 'swab test' he recently took.
The 17-year-old even referred to Mariah as a 'weasel'.
He said: 'I think I could smell a weasel a little bit.
'It's pretty crazy how people make up false accusations. But I'm 17 - it's going to happen, being in the spotlight.'
Bieber, who is currently dating Disney star Selena Gomez, 19, dismissed the baby allegations, saying: 'People can say whatever.'
When asked if he had taken the paternity test, the Canadian singer said: 'Yeah, I took it.'
Asked if he had to take his clothes off, Bieber added: 'No! They just swab your mouth.'
Mariah Yeater, 20, recently claimed that Justin is the father of her four-month-old son Tristyn.
With the U Smile singer doing a swab test earlier this week, according to US website TMZ.com, it is now up to Yeater to submit her baby to a DNA test.