I have opted for commerce with maths in class 11th. Can I pursue BCA?

Dear, As BCA is a 3 years degree course - after completion of your +2 in commerce with mathematics, you can pursue BCA following the marks and other eligibility criteria of the institute, you intend to get admission. Best wishes.

Yes, you eligible for doing BCA.

Normally, BCA student must have science in 12th but now in many colleges, they also accept commerce student with computer application subject. So if you have computer application then you can get some colleges with computer application subject.