hi,

see to get admission in computer science related course you have several options,

you may do b.tech in computer science

or bachelor in computer application in computer science

or bsc in computer science,

either of the way you go , the basic eligibility criteria is you must have studied mathematics in 12th course, now you may join nios and appeared in only mathematics papers for nios course, since nios  comes under recognized education board and students may apply for only one subjects in nios course.

Hope it would help.