Yes off course a Biology student can join for B.Tech Computer Science only when you have opted for maths as an additional subject.

Biology student have the option of selecting either Medical or Engineering that's the added benifit of the course, since Physics, Chemistry is already there along with Biology which is also needed for Engineering course but you should have maths as  an additional subject then only you can opt for engineering otherwise you can't.

So if you are interested in doing Computer Science course and feel that you have not scored good marks to apply for medical then you can go ahead and apply for Computer Science course in some best college.

You can prepare yourself for competitive exams like JEE mains and scoring good marks will lead to more options and more wider selection for colleges.