Dear Shital ,

National Institute of Open Schooling widely known as  NIOS  is a central education Board established by Ministry of Human Resource Development (MHRD) and is equivalent & at Par with CBSE, ICSE and GSEB .Yes , the certificate of NIOS is valid for MBBS and Bds admission .So ,dont worry regarding your certificate is valid or not you should focus on your entrance test .

Hope it will helpful and best of luck .

Thanks