My father had prostrate surgery and had a catheter which was removed 3 days ago. He still has blood in his urine. Should he go to ER or wait till Monday to call Dr?

He should call his family doctor's answering service and leave short message (blood still in urine). The doctor or covering doctor will call him. I see no reason to go to the ER as you state it. Usually this is covered in the discharge papers. Is there no mention of what sorts of things he might experience?
(PS: prostate, not prostrate, which means lying down)

If he can see blood in his urine it is cause for concern and can be caused by an in line catheter, improperly removed at times. He could be experiencing a urinary tract infection. Hard to say not knowing the exact particulars. If it eases your mind, take him to the hospital.