The 34-year-old actress appeared on Thursday's episode of The Ellen DeGeneres Show following her engagement to Jost, an actor and writer for Saturday Night Live.
"He killed it!" Johansson said of Jost's proposal. "He did like a whole James Bond situation. He's surprising. He's got a lot behind that news desk that he's hiding ... [He's] very charming and very thoughtful and romantic.
"I was surprised," she added. "Even if you kind of imagine what that moment's going to be like, it's a beautiful moment."
Johansson didn't share the specifics of Jost's proposal but said the moment was very meaningful.
"It was very personal," she said. "It was a very special moment. I think more than anything, when someone tells you they want to share the rest of their life with you, that's just a lovely, special thing."
Johansson and Jost got engaged in May. Johansson showed off her 11-carat engagement ring during an appearance at San Diego Comic-Con in July.