L.W.
No, but the benefits of either are relatively the same. The treadmill is constantly moving. That motion actually takes away a very small amount of resistance. That is why runners who train on treadmills get winded and tired if they try the same workout on the road.
However, walking on the treadmill will give you exercise and the benefits far outweigh the resistance benefit. Walk outdoors when you can, but it is more than okay to walk on a treadmill out of the weather.