I think this would depend on the particular school and department you are considering applying to. That being said, if you already have taken some computer science courses as part of your undergraduate degree in math and have otherwise met the admission requirements for the program, I don't foresee any problems with your being admitted to and earning a second Master's degree in computer science.
My suggestion would be to visit the website of the computer science department of the school you wish to apply to and check their admission requirements. Also try to speak to a registrar about any other specific questions you may have.