Students passed out from NIOS board can write any competative exam, you are eligible to apply for any of BALLB enatrance exam you will not face any problem in future also. There are the entrance exam on national level like CLAT or other  university level exam like BLAT, AMU BA LLB etc. To know about CLAT you can go through with given below link.

CLAT Eligibility

In case if you are interested in any other exam let me know.

Good Luck!