He may be suffering from anxiety. Is he yelled at for things, or spanked, or teased by others? Has anybody ever said hurtful things to him out of anger? Are there expectations of him that are yet beyond his abilities or understanding. Does he get a lot of hugs and praises for his efforts to do things right, or when he behaves well, when he cleans up his room the best he knows how, even when it may not meet his parent's standards? Is he happy with going to school? Does he enjoy playing with the neighborhood friends? Does he feel confident to try new things that will build his self esteem and confidence? This is an age where a child needs a lot of love and attention from his parents and relatives. He will go for it whether it is good attention or bad attention...it is still attention. Is he feeling threatened that he may play second fiddle to sibling's attention getting, or mom's new boyfriend or Dad's new woman in his life? Just some things to think about. Stuff like this can create anxiety as he is too little to mentally figure out things and answers to his problems.
Speak to a child psychologist first. They could determine if its maladaptive behavior or ocd and if a referral to a chld psychiatrist is needed or if cognitive behavioral therapy would work.