Dear applicant if you follow the eligibility criteria of M.Sc Computer Science course, then you would observe you need complete your Bachelor's degree in any of the Science stream from a recognised university of India. Since you had B.Sc in mathematics hence you are eligible, based on your merit or you can also appear in entrance tests like JNUEE, BHU PET, DUET etc.

https://www.careers360.com/courses/msc-in-computer-science

Good luck!!!