Is something wrong with my 13 month old?

My son is 13 months old and sometimes he responds to his name and sometime when other people calls him, he ignores them or doesn't respond to them. My parents and siblings (who have all had children) thinks that there can be something wrong with him, and it's really become unnerving. When I take him to the doctor the doctor says he's perfectly fine. So I was wondering if anyone else may have had this problem with the child? This is my first.