The National Catholic Reporter has published an article about Maryland's anti-terrorist database and the implications of having incomplete or inaccurate information included. The case of 2 nuns who participate in anti-government actions is highlighted. I must note that one of the commenters alleges that one of the nuns spent 2 years in jail for breaking into a nuclear facility. I haven't checked to see if it is true, but without knowing the circumstances around the event I can't agree that it makes her a terrorist.
The bigger issue here is that protesters who are exercising their rights under the law will be characterized as terrorists or potential terrorists in some database. This data is difficult to get hold of, for obvious reasons. If it is inaccurate or incomplete that makes it extremely dangerous, and raises the question of its overall reliability. We are talking people's lives and reputations here. You may recall that Senator Kennedy was on the no-fly watch list because his name got confused with someone else's. It took a long time to fix that issue. The price of freedom is vigiliance, and that includes watching those who would watch us.