I pursued diploma in mechanical engineering. I am now in second year of mechanical engineering. Can I apply for BA?

I think you are not eligible. you need to complete 10+2 to apply bachelors in art. mechanical engineering with BA is not a good idea.

You will be an engineer in next 2 years. Why do you want to do BA ? Eligibility for BA is +2 from a recognized board. Diploma is not treated equivalent to +2 by most of the universities. Therefore, as diploma holder you are not eligible for BA course.