Make sure the key fob isn't getting mashed in your purse or something like that. mine has gone off once when I was walking across the parking lot. I had my cell phone in my pocket with the fob and it mashed the panic button.
Welcome to our forum LizM! Do you have the windows down or somewhat open? You did not indicate your trim level, but if it is an L2 or L3 then you have the more advanced alarm system which includes an interior sensor. If the windows are down you could be having something fly through and trigger your alarm.