I'd suggest that your air-bag sensor has decided that it's time to go and have the airbag system serviced. It's best to have a 'pro' look at that....either that or remove the airbag and get a 'killer' steering wheel and live dangerously!
There was some discussion about this on the digest not too long ago. I think Alex is right. The airbag is supposed to be serviced/replaced after 10 years.
I think that it would be ridiculously expensive to do, haven't had to deal with this yet.