Sort of. They definitely had a concept of doing something that might be virtuous if you did it a little bit, but is crazy and bad if you do it too much. Plato's Crito is a great example. Crito is written as a normal person with normal values. He thinks that Socrates is great and it's great that he respects the laws so much, but it's crazy to die for that belief when he could escape. He seems to think that Socrates is something of an extremist: its not that respecting the laws is bad, it's just that you're supposed to balance that against other things, like taking care of your family and helping your friends.

This is not the same, exactly, as an extremist who wants to go out and hurt other people for the sake of their ideology. There are certainly very old examples of that in the bible, but I'm not thinking of any in Classical Greek sources