The reason that you're taking beta blockers might make a difference. If, say, you've been taking them (either on their own or with other drugs) for blood pressure problems then, if the doc is satisfied that they're no longer needed, I can't think of any reason why they couldn't be immediately stopped (with no ill effects).
However if you've been taking them to help you cope with anxiety then a common sense approach would seem to suggest that it might be better to come off them gradually.