Don't know if this is the answer, but...
I had an airbag lite about a year ago, the ford dealer chased down the problem and it had to do with, get this, the driver seatbelt lock. I guess with the newer Explorers it senses if the driver is wearing a seatbelt and deploys the airbag accordingly faster if you not wearing slower if you are. I asked when this lite was on if it would deploy when it needed to and he said that it might NOT... So i would look into it as soon as ya can. But, like I said that was just my problem I sure there is a ton more faults that could cause it though. But if your depending on the bag for safety, I would get it looked at