Rip just answered an identical question in his main QA section. Dips are not in the OW program. In fact, I don't recall seeing dips in any of the basic programs for novices.
This is probably because benching and OHPressing (alternating every session) will be sufficient stimulus to develop the muscles you would hit during dips. As lifts begin to get more difficult and your proficiency rises, adding assistance work makes sense.
I will assume that you are at a point were this would make sense in your training. I personally find dips to be alright on Press days, but struggle more on Bench days. YMMV.