That very well may be a pecked groove, but it's hard to tell from the photo. Can you post a profile picture of the piece with the entire groove visible? Thanks.
Back the camera up a little bit (it's focused on the key board not the rock.) Most digital cameras do better over a plain background vs busy backgrounds where they try to autofocus on something with contrast (in this case black keys with white letters.)
Looks like a 3/4 groove hammerstone or Axe preform...................good find, I would have took it home...................... ...............GTP..........
I forgot to mention how I found this site. I was out ginseng hunting when I seen smoke signals to the east. I located the smoke source and sure enough---right between two tepees, next to a totum pole I found this arrowhead!