Hii..

Candidates wishing to pursue the course are needed to fulfill the minimum eligibility criteria listed below in order to apply for the course:

• Graduation (B.Sc. (Bachelor of Science)/ B.Tech. (Bachelor of Technology)/ B. E. (Bachelor of Engineering), with Mathematics as one of the main subjects, completed from a recognized university.
• A minimum aggregate score of 55% or equivalent CGPA at the level of graduation (relaxation of 5% to SC/ST candidates).
• Often, a minimum of 1 year of work experience, as many institutes prefer students with professional experience.

Thus you are eligible for MSc mathematics although you have done your BSc in computer science.

Hope it helps. 

Best of  luck