Yes you surely can appear for the upsc exam after doing bsc course. The basic eligibility qualification required for getting into IAS is that the candidate must hold on a graduation degree from any course from a recognized board or university.

The age criteria is minimum 21 years of age and maximum 32 years for general category and the number of attempts you can give is 6.

Rinku, the eligibility to appear for UPSC exam is to complete your Graduation in any discipline. Which means that there is no specific stream that you need to complete your Graduation in. So just to  answer your question, you can appear for UPSC examination even after pursuing B.Sc.