Hello Prashanthi, 

Of course, an OBC can apply for seats under the Open category in the CSAB round. In the Open category, candidates from all categories, be it General, SC, ST or OBC can apply as there are no restrictions or borders on any category in the Open category, as the name itself suggests. Although, if you do need your OBC certificate to meet the cutoff, you might apply that to your advantage.

All the Best!