Atticus does his best not to show his fear. He deliberately and slowly creases the newspaper. He talks slowly, moves slowly, and his voice doesn't change. When Scout shows up, he shoots her an angonized glance. Scout says "A flash of plain fear was going out of his eyes..." (pg 154) When the men confront him, Atticus puts the newspaper down "very carefully" and then Scout notices that his fingers were trembling a little. When the men leave, Atticus goes to the jailhouse wall and leans against it with his face to the wall. He takes out a handkerchief and wipes his face and blows his nose violently. One can infer that he shed a few tears. All of these actions indicate that Atticus was frightened. He was one person facing a mob, and his children were in the middle of it.