I found a cockroach in my bathroom?

I live in a fairly clean apartment building.. Lived here for two years and in my time here over the coarse of the last 6 months I've seen 4 cockroaches 1 in my kitchen, and three in my bathroom.. The first 3 were in the same 2 months where as this last one is the first I've seen in about 4 months. they are pretty small..should I contact an exterminator? Or could the roaches be just passing through? There are no droppings.. I just need advice lol!