Quick Answer: Yes, bell peppers do cause gas.
Bell peppers are rich in fiber, glucose, and fructose. Your intestines can have difficulty breaking down and absorbing all of these.
What the stomach can’t make use of, it passes on to your colon. Naturally occurring (healthy) bacteria in the colon ferment these carbohydrates to further reduce their volume. Two byproducts of this process are hydrogen and methane gases.