Flames into cooking area
Not really normal to see it happen frequently, though I have seen it happen in commercial convection ovens when they attempt to recover to a high heat. Or, simply, the oven was at 200 - 220 celsius, then the doors were opened letting out all the heat while pans were rotated, then the doors closed and the oven started to recover and heat up again while the fans were spinning up. You ended up with little 'poofs' of gas that ignited. 

Throughout normal operation, however, it wasn't something you'd normally see. It worries me enough that my best advice is to discontinue use until you've been able to contact the manufacturer, or a repair place that's authorized by the manufacturer. You could have a faulty internal regulator which is something that can be pretty dangerous. It could also be a faulty part in your gas meter, which is a matter you'd need to discuss with your utility.

I'd turn it off, and get on the phone.