I see these predatory mites from time to time; a lot of times when little else in the way of insects or arachnids is present. But, some very tiny beings must be present for these guys to prey upon. Usually, as was the case with this one, I find a solitary individual running around up and down the stems and leaves of a plant (in this case pelargonium carnosum), pausing infrequently and then running on.
I do not know what species these guys are; they are much larger than the plant-sucking mites (maybe 1/16 inch or so). Anyway, I find them interestingly enigmatic.