Depends on the state you are in. In tamilnadu majority of christians are OBC. In Kerala certain Christian communities come under forward community and hence general category

Greetings of the day dear aspirant

As Christianity is a religion and not a caste, it will not be under category like General, OBC, SC or ST. They will be under religion. But again under religion we have minority religions and majority religions. And since the number of Christians in India are very less, they will be under religious minority not category.

You can have a General category person and be a Christian. You can even have an OBC or SC or ST who is a Christian. On the other hand you may also find ST/SC/OBC/General who is Hindu. Religion and category are two different things and should not be mixed with each other. However, Christians comes under minority community in India as their population is very less.

I hope this helps you!!

All the best for your future endeavours