Bieber's Alleged Baby Mama THE MUG SHOT

11/4/2011 4:23 PM PDT

TMZ has obtained the mug shot for the woman who claims she's Justin Bieber's baby mama ... taken moments after she was arrested for allegedly slapping her ex-BF last year ... the OTHER guy she accused of fathering her child.

As we previously reported, Mariah Yeater was charged with battery in December 2010 for slapping her ex-BF John Terranova ... after she told the guy he was the father of her then-unborn baby.

John claims the baby isn't his -- ditto for Bieber.

Yeater is due back in a Vegas courtroom in the near future.