Its true, Maint Req'd is the oil. I would actually not hard reset the computer like others suggested unless you're xB is not a DD that you've got time to mess with.
I would drive over to Toyota (if you trust the dealer) and have them plug it in. After that, go to a local Advanced Auto Parts (or similar) and have them plug it in. If both have the same response in why the light's on. Go with that. If the dealer says its nothing, just have them reset the light. Going through the dealer will keep everything on file, so to speak. If they tell you its nothing and it becomes something, you're covered.