From a report by the Council On Foreign Relations:
"The FBI reports that eight of the fourteen terrorist acts prevented between 2002 and 2005 were planned by right-wing groups. The others ranged from an anarchist plan to bomb a Coast Guard station, a prison-gang attempt to attack military and Jewish targets around Los Angeles, and a few people who attempted, individually, to establish ties with al-Qaeda."

and more:

"Although environmental extremists were responsible for nearly all the domestic terrorist attacks between 2002 and 2005, right-wing extremists are still considered the most dangerous to the United States, says the SPLC. Right-wing extremist attacks are planned to target people, and if successfully carried out, intend to kill many civilians. Ecoterrorist attacks, on the other hand, aim to sabotage the infrastructure of businesses and corporations that endanger the earth; the groups do not aim to kill massive amounts of people.
The FBI says right-wing extremists have the potential to carry out the most deadly domestic attacks since they have a tendency to amass weapons and explosives and have "a propensity for violence."


Please don't believe me - read the whole thing.

http://www.cfr.org/publication/9236/#p7