If it's a swarm, they will likely move on within a day or so. This is the time of year when young queens head out to start a new hive. Keep an eye on them, but most likely they will be gone by tonight.
If you live in an area known for the africanized bees, that's a different problem. That would have me calling in a professional without any debate. If you can't find anything in the phone book, contact your county extention agent (google "your county" county extention). Someone there will be able to give you both bee keepers' names as well as a number to call if you are concerned about the african bees.
I'm violently allergic to them, but I try not to chase any off because I need them for the garden. I'd have hives for honey if it weren't for the allergies. In any case, good luck!
at 2:15 PM on Mar. 12, 2011