As far as I know, you are eligible for OPT each times you graduate from an institution. So, that means you will be able to work in OPT again when you finish Bachelors and then another one after masters degree too, if you considering to go to graduate school also.

However, I recently was told that you can extend your OPT by 17 months(provided that your course of study is under STEM degrees and working for organization enrolled in e-verify program) only once as a F-1 student, irrespective of level of education, and you can do so only after you at least have Bachelors degree.