Well, I just got chicks for the first time recently but I watch them all the time... from what I see and from what I heard from a local farmer, there seems to be a pecking order, so it's possible that s/he could be establishing her/himself as a higher up... it seems that pecking amongst each other is fairly natural and not necessarily bad- as long as it does not get out of hand or as long as one chick isn't getting the brunt of everything. One of my Golden Comets pecked at all my other chicks when we put them together but stopped after a while and no damage was done...
I'd definitely keep an eye on them to make sure no one is harmed though. It is definitely frustrating when they peck each other! Today my Rhode Island Red roo (he was supposed to be a hen :/) pecked my favorite Golden Comet in the eye.. she's okay but it's pretty irritating!
How old are the chicks? Pecking is definitely not just a roo thing. The Golden Comet that I mentioned that pecked at all the others is a feisty little hen (that breed is sexed by feather color as chicks) so yeah o;
Anyway, now I'll let more experienced chicken-owners come in and tell you what they think [nod]. c: