maggie used to do this but she has gotten used to it (sorta). she pretty much sits there and lets me brush her. i try not to take her from playing with her toys to do it cuz then she is worked up and it's not fair to make her chill while she is in play mode. but she does once in a while try to bite the brush. we have taught her the "no bite" command and I use it while brushing her. it usually works.
when she was that young, I would give her a different brush to chew on while I used another one to brush her. she was usually happy with that. she just wanted to attack a brush
good luck..I hope it gets better. your baby will get used to it eventually. just stick with it.