Err... is there a legal recognition of hate groups in the United States? The FBI probably has a list, but they don't publish it.
If you are a part of any radical group of extremists or are associated with any group of radical extremists, the FBI can and will keep tabs on you. Meaning they will be watching your every move and possibly with two groups of people if you're really important.
What you want to look out for if you're being watched at first is the decoy team, which focuses on making sure you catch them while they work on the whole aggression tactics that are designed to simply piss you off and get you to make a mistake of some kind. These tactics range from following you to blocking your path to motor vehicle collisions and can be pretty dangerous as they are supposed to piss you off.
Once you notice someone is following you, confront that person with the help of another friend and ask questions. Write down everything and make sure that if they really are following you that you are hopefully prepared to deal with the stealth team. That is the second team that goes into action then the decoy team is lost. Their job is to watch you, and these spooks will not be seen or heard as it is their job to go unseen.
Of course in this day and age if you suspect you are being watched or monitored by the FBI you can thanks to the Freedom of Information Act request your information record from the FBI with a notarized letter. They will send it to you in due time but you might have to pay a fee to get these records. Of course, you can state how much you are willing to pay the FBI for these records in your notarized letter and they will accept it. However certain things will be expunged or redacted as it is the government you are dealing with.
Either way if they start watching someone it's usually the day they get the information about the person they are supposed to watch and it can go onwards for about ten to fifteen years at most before they decide to stop watching your every move. If of course you get one of those tracking devices planted on your car like someone on Reddit, please be sure to mail it to some far-off country like France or Israel just to fuck with them as unless they have a warrant they are not allowed to place those.
I am happy I know this from the week I spent researching everything I could find about the FBI after the paranoia hit me thanks to a false report getting me permanently banned from 4chan. I am also happy that if I manage to save my money this week I might be able to buy a couple cheap yangire-themed anime DVDs in the next week or two - and that I have a plan to do just that.