It varies depending on the intensity of the workout. Blood pressure is supposed to go up when we exercise, that is normal. How high is too high, I don't know. Depends on age, conditioning, etc. Check with your doctor if you suspect yours is running too high.
I generally get nice and low (for me--120s/80) readings after a hard cardio workout. I take it within 15 minutes to an hour after stopping. I have no idea what my BP would measure during exercise; it would be awfully hard to take it while doing the actual workout.