If you reject federal authority in favor of state or local authority... you might be a terrorist.
If you don't believe in restrictions on firearms ownership and use... you might be a terrorist.
Otherwise, you may just be a right-wing extremist:
"I&A (DHS Office of Intelligence and Analysis) will be working with its state and local partners over the next several months to ascertain with greater regional specificity the rise in rightwing extremist activity in the United States, with a particular emphasis on the political, economic, and social factors that drive rightwing extremist radicalization."
Click the link to get to Michelle Malkin's story. She has a link to the actual document too.