Well, the Assyrians (2,500 BCE - 605 BCE) were reknowned for their use of terror tactics - they would launch the heads of slain enemies into walled cities as warnings (and to spread disease), amongst other things; this link will give you some further insights: http://www.ancient.eu/Assyrian_Warfare/

There was the Asiatic Vespers in 88 BC, thousand Romans where killed in many cities in asia-minor on the same day.

The Jewish group more commonly known as the Zealots were a first century anti Roman and their collaborators terrorist organization. Based primary in Jerusalem. They were also called the Sicarii after the small knife that was their main weapon of choice. Their preferred method of attack was to approach the chosen victim in a large crowd stab quickly then melt back into the crowd.They were widely feared both by Romans and fellow Jews.