The Mother's Day actress, 46, waved her arm and appeared to say "move" and "watch out" when Theroux, 44, and his Leftovers costar Liv Tyler walked on stage to present the Best Sci-Fi/Horror Movie category.
Clad in a dove-gray Saint Laurent dress, Aniston also stole the show with her hilarious reaction to Kate Beckinsale. The Friends alum appeared worried (did Beckinsale slip on her dress?) when the Underworld 5 star, 42, walked across the stage in a sparkly silver Monique Lhuillier gown.
Aniston was on hand to support her man and his HBO series on Sunday night. (Theroux lost out to Mr. Robot's Rami Malik for Best Actor in a Drama Series.) An onlooker tells Us Weekly that they mingled with Last Man on Earth costars and exes January Jones and Will Forte, and Theroux even posted a hilarious selfie with the Saturday Night Live alum, 45.
"Always awkward bumping into Will Forte," Theroux captioned an Instagram photo. "Half the time he's so sweet. The other half he acts like a total psycho." Forte stepped out with only half of his head and face shaved, possibly a stint for his dystopian comedy on FOX.
Watch Aniston's amazing reactions above!
Sign up now for the Us Weekly newsletter to get breaking celebrity news, hot pics and more delivered straight to your inbox!