Suggest Treatment For Brown And Large Spot On Head

We just found a very dark brown, round, flat, smooth, the size of a large pea, spot on our sons head (he's 10). The very outter edges look slightly lighter brown but not much. We're not sure how long he's had it - as he just got a very short haircut and therefore we noticed it -- his last short hair was perhaps 6-8 weeks ago - so he may have had it then - but it may have been smaller and we just didn't notice it. Should we be concerned?