This study examined the behavioral patterns of Japanese extremist groups, based on 377 terror incidents that occurred in Japan between 1990 and 2010. These incidents included bombings, rocket attacks, hostage taking, and vehicle assaults. Information was drawn primarily from on-line newspaper databases. A multiple correspondence analysis was performed using five categories: extremist group identity, time of attack, target of attack, attack strategy, and method of claiming responsibility. Extremist group characteristics varied along two dimensions: the interaction level between terrorist and victim, and the indiscriminate level of use of force. We categorized multiple far-left, far-right, and religious extremist groups based on these two dimensions. Our findings may help prevent terror attacks, and help identify the group responsible for a given incident.