I agree with Elizabeth, it is probably a swollen lymph node. Though if it does in fact feel like bone, it could be the mastoid process you are feeling, part of the temporal bone of the skull and a site of muscle attachments. It is possible for this bone to become infected, mastoiditis, though not common.
I agree, if it persists for any length of time, gets larger or becomes tender to touch, have it examined by a doctor. Though it is probably nothing much to worry about.
Take care.
