Definitely keep exercising!
Actually, depending on how high your blood pressure is, it may be more important for you to shed the pounds then stay on the beta blockers (talk to your Dr. before doing anything dramatic though!).

There is a really great guide about exercising with hypertension put out by the American College of Sport Medicine.

You will find that beta blockers are notorious for interfering with your body's ability to perform during exercise, which is why athletes rarely take them. You may want to discuss other treatment options with your doctor.