Yes, it is a crime - and the punishment is deportation.
8 U.S.C. 1227 (a)(1)(C)(i)
Nonimmigrant status violators.-Any alien who was admitted as a nonimmigrant and who has failed to maintain the nonimmigrant status in which the alien was admitted or to which it was changed under section 248 , or to comply with the conditions of any such status, is deportable.