The gas that you fart out is indeed flammable and can actually be set on fire.
When you fart the gas that comes out is composed of gases including methane and hydrogen and those gases are flammable especially the methane.
As a kid I remember a friend set his fart on fire and it actually did set on fire just for a short time but the fire goes out really quick.
So you could get burnt from the flammable farting gases when setting them on fire but it's not likely to harm you much.
The fire extinguished itself really quick when he set his fart on fire as a laugh and he was okay.
I would not recommend setting your fart on fire though but it certainly is flammable when you fart.