The US Department of Defense defines terrorism as the following:

terrorism — The unlawful use of violence or threat of violence, often motivated by religious, political, or other ideological beliefs, to instill fear and coerce governments or societies in pursuit of goals that are usually political

It's often hard to pin down what groups did what in the run-up to the American Revolution, especially since groups of the same name operating in different states often had little in the way of coordination, much less a unifying central authority.

But in the specific case of the Sons of Liberty, specifically the Massachusetts chapter, there's not really a better example of political activism turned terrorism than the treatment of Andrew Oliver. The Sons of Liberty claimed to have grievances with the Stamp Act and effectively took their frustration and anger out on Oliver, first burning down some of his property, then beheading and then burning him in effigy, then throwing stones at his house, and finally vandalizing his home.

If it ended there one might make the case that this was simple an isolated event. It didn't. Oliver's brother-in-law (then the Lieutenant Governor of the colony, Thomas Hutchinson) was harassed. Oliver was eventually forced to resign publicly (it's hard to imagine that coercion wasn't involved). Since all of this happened before he was legally appointed, he was eventually forced to resign yet again a few months later (after the royal appointment arrived), this time with the requirement that he swear to not take up the job in the future.

So, to summarize, a group styling itself the Sons of Liberty destroyed (or stole) significant amounts of Andrew Oliver's personal property, effectively laid siege to Oliver's home while he and his family were present, and then forced him, under duress, to resign his legal appointment (both before and after it arrived). That's pretty clearly the use of violence in pursuit of a political agenda (in other words, terrorism). And I suppose McIntosh, the ringleader in all of this, can probably be charged with fomenting a riot, too.

If you're looking for more sources, I suggest Justin Winsor's The American Revolution, which relates this story (and others) to provide a less rose-tinted history of the American Revolution than we get in primary school.