Can i prescribe beta blockers in post-coronary artery bypass surgery with lbbb patient?

Yes depending : None of those are contraindications, but as always it's risks vs benefits as it applies to the individual patient.

Yes: Beta blockers are strongly indicated in a post CABG patient. The vast majority of patients with a left bundle branch block (lbbb) will tolerate them well. If there are other arythmias (second degree heart block etc) much more care would need to be taken.