Before you take it to Nissan, try the below method.
Turn the key to the on position and watch the airbag light. It should stay solid for 5-7 secs, and then turn off, and then start to flash.
To reset the light, you must turn the key to on, watch the airbag light stay solid for 5-7 secs and as soon as the airbag light turns off, turn the key to the off position (you have to turn the key to off before the airbag light starts to flash, or you must start over). You need to repeat this 5 times. Try to start the car, and hopefully the light will be reset
Had same problem last month...above fixed it. No more flashing airbag light.