Farts happen, and passing gas is quite common while practicing yoga. We move our bodies in ways that shuffle and relax our intestines, and nature takes is course.

You could reduce your gas symptoms by waiting at least four hours after eating before doing yoga. Traditionally, yoga was practiced first thing in the morning.

Or you could accept that a few minor releases are part of the experience. Talk to your teacher about the etiquette she or he would suggest for your class.
 
You're not alone, by any means. Film star Mike Myers was recently kicked out of a Los Angeles yoga class because he couldn't stop giggling when a mat mate farted. "I am not very mature... if somebody farts, it's funny," Myers told tabloid reporters in mid-2007. "They were like, 'We're not here to laugh.' but then he did it a second time, louder, and did it a third time and it sounded like a machine gun and I could not stop laughing."