Yes, you need to address the lights, your mechanic is correct in that if the light is on then the airbag MAY not go off in the event of a collision. (It could be something as simple as a faulty switch at the seatbelt.
An intermittant CEL is usually an indication of a faulty O2 sensor. But could indicate a more severe problem (possible cam sensor gone bad, etc.) Autozone is reading codes for free these days so drive down if you have one near and find out what is wrong.
"It's not because I'm an aggressive driver, it's because I'm an idiot" actual quote from my wife.