D.W.
It's not completely average, but it is definitely possible.
I recall reading in one of my baby or pregnancy books that some babies are born with teeth - a little creepy but possible.
You may want to call the pediatrician just to be safe in case it's something else.
But, the science is definitely there in rare cases - ~1/2000 according to BabyCenter.com (see link below).
http://www.healthychildren.org/English/ages-stages/baby/t...
http://www.babycenter.com/0_developmental-milestones-teet...