Yes you are eligible to get admission in MCA after BSc in Mathematics.
But you need to write some MCA entrance tests to get admission in the good colleges.
I am mentioning some tests here
Jawaharlal Nehru University
Maharashtra Common Entrance Test
Punjab University MCA Entrance Test
All India MCA Common Entrance Test
Banaras Hindu University
West Bengal Joint Entrance Exam MCA
NIMCET
VITMEE

Here I am also providing you list of some good colleges for MCA
Banaras Hindu University
BIT,Mesra,Ranchi
Cochin Univ of Science & Tech
Jawaharlal Nehru Univ(JNU),Delhi
NIT Allahabad
NIT Bhopal
NIT Calicut
NIT Durgapur
NIT Jamshedpur
NIT Kurukshetra
NIT Raipur
NIT Surathkal
NIT Trichy
NIT Warangal
Pondicherry Central University
University of Delhi
University of Hyderabad
University of Pune
VIT University Vellore