Well it looks like everyone has a different take on when to increase outside physical activity.I am assuming you are doing Da Vinci Surgery.
DJhouston says you should walk a mile a day with the catheter "IN". I think that might be too much too soon. I think He had his catheter in for four weeks, the usual catheter time is about 7 days. so the first week after surgery you should really just do cautious walks around the neighborhood. After your catheter is out increase your exercise slowly to a comfortable level. The area to protect is your abdominal muscles. So don't lift heavy things (more than a few pounds) and don't do sit ups.(don't help your wife vacuum the house..lol) Do walk and climb stairs.
At about week three or four, if you are an active person, you are going to want to test yourself. Don't do it. You have nothing to prove. If you were a marathon runner before, you will want to begin to run. (read other posts), If you were a weight lifter before it will be harder, but protect yourself for at least 6 to 8 weeks post surgery.
If you were sedentary an/or overweight before, start slow...but this is a great time to start getting yourself in shape.
Many guys go back to work 3 or 4 weeks after surgery. I know it was glad to have more time off. For many the biggest problem going back to work is incontinence.
I play a lot of golf and my urologist said NO golf until after the 6th week post surgery. I am back to golf full time now 3 or 4 rounds a week. No major problems, except a bit of leaking. I am doing yardwork and stuff but I still try not to lift anything too heavy because of many reports of post surgery hernias. I am 11 weeks post surgery and go next week for my 1st post surgery PSA test. (every doctor is different).
My advice ...stay active, but don't strain or overtax yourself.