I've owned two 2012 Civic Si coupes, and I've driven a rental Civic LX sedan extensively while getting premature warranty work addressed on the second Si.
Before my first Si was totaled by a teenager running a red light in March, I had the issue you are describing. If someone shifted to either direction (as if to turn around and look behind them), the light would go on turning the Passenger Air Bag off. They'd resume 'normal' position, and it would go away. I admit, it concerned me, as my 2006 Civic Si had multiple airbag failures (despite never being in an accident). However, I ultimately learned that it did not impact the airbags when the kid hit me: it's just very sensitive.
My second 2012 Si does not exhibit this, nor does the LX sedan I have as a rental. Strange? Personally, I've had a lot of quality related issues with the seats in my cars (popping, clicking, plastic sounds from seat backs, squeaking seat cushions), so the sensitivity isn't a surprise to me.
Ultimately, I think you're fine - it's just an annoyance.