Although Montag does not confront Beatty -- the symbol of oppression -- until the end, he takes deliberate steps to distance himself from society long before. He claims that "his hands" acted on their own, stealing books, but it was actually his unconscious curiosity that gave him the impetus to steal and hide the books in his own house. That act alone makes him rebellious, but it isn't until after Beatty lets him know that he is under suspicion that he moves from passive to direct rebellion:
"There's only one thing to do," he said. "Some time before tonight when I give the book to Beatty, I've got to have a duplicate made."
"I can get books."
"You're running a risk."
"That's the good part of dying; when you've nothing to lose, you run any risk you want."
(Bradbury, Fahrenheit 451, Google Books)
Montag has a fantasy of copying books, making more, hiding them in the houses of firemen so as to break up the stranglehold of firemen on society, but he quickly understands that there is no point. He is only one man against a whole government structure based on opposing his ideas. Instead, he tries to rebel in a more seditious way, reading poetry to his wife's friends, and finally killing Beatty and escaping the city to help spread the small knowledge he has memorized.