A quote of a from the New York Times, based on statistics provided by the US Military Academy's Combating Terrorism Center.
Despite public anxiety about extremists inspired by Al Qaeda and the Islamic State, the number of violent plots by such individuals has remained very low. Since 9/11, an average of nine American Muslims per year have been involved in an average of six terrorism-related plots against targets in the United States. Most were disrupted, but the 20 plots that were carried out accounted for 50 fatalities over the past 13 and a half years.
In contrast, right-wing extremists averaged 337 attacks per year in the decade after 9/11, causing a total of 254 fatalities, according to a study by Arie Perliger, a professor at the United States Military Academy’s Combating Terrorism Center. The toll has increased since the study was released in 2012.