Unfortunately, it is not uncommon. Between 1967 and 1974 the country was ruled by a right-wing military junta, from which Golden Dawn claims continuity. (Ironically, the junta's 1967 rise to power – by arresting politicians and military figures – was the last time a Greek party leader was arrested before today.)
Greece also has an active far left. After the war, the country came very close to aligning with the Soviet Union, with a vicious civil war fought from 1946 and 1949 between the US- and British-backed military and the Greek communist party.
Later, far-left terrorist groups appeared, including the Revolutionary Organization 17 November (17N), initially fighting military rule.
Named after a 1973 university uprising, 17N engaged in a campaign killing and kidnapping for decades, including the Dec. 23, 1975, assassination of Richard Welch, the CIA's station chief in Athens. Until 2002, Greek police had not arrested a single member of what was one of Europe's most elusive terrorist organizations. But that year, a government crackdown saw the arrest of several members of the group, including leader Alexandros Giotopoulos, who worked as an academic.
In 2007, another group, Revolutionary Struggle, fired a rocket propelled grenade into the US Embassy in Athens. Since 2008, anarchists have attempted to firebomb car dealerships and banks.