Credit: Getty Images; Gilbert Carrasquillo/FilmMagic

Justin Bieber may have a doctor's appointment visit on Friday --- to take a DNA test disproving he's the father of Mariah Yeater's son Tristyn, 4 months.

"He's ready to take a paternity test, at any moment. We have one scheduled for tomorrow," Bieber's manager, Scooter Braun, told Extra host Maria Menounos at Thursday's Pencils of Promise charity event in L.A.

The announcement is a surprise, since Bieber is not obligated to take the test. Yeater had claimed that she had sex with Bieber, now 17, backstage at an L.A. concert in October 2010, but she dropped her much-scrutinzed paternity suit last week.

Braun explained that Bieber "doesn't mind" taking the DNA test. "He's like 'I'm just going to go ahead of it and be fine.'"

The "Baby, Baby" singer himself added: "It doesn't matter."

And the pop phenom's team is still considering legal action against Yeater, Braun hinted. "We've never even seen the lawsuit, but we're going to just get ahead of this thing and go right after it. I think it's important to hold people accountable for their actions."

Added Bieber (currently dating Selena Gomez): "We don't want it to seem like its okay for everyone to say, like, 'I had Justin's baby or having his baby.'"