You must produce a caste certificate as and when asked for it. It can be used for reservation in educational institutes, jobs, etc. The problem is that when you apply for a central government job, you have to produce your OBC caste certificate which has been issued by the state PSC (Public States Commission, Bihar in your case). Accordingly you will have to acquire your certificate from the National Commission for Backward Classes (NCBC). If you belong to the non creamy layer according to the NCBC, you will be considered in the general category.