The pair were filming the Marvel movie on the Canary Island of Fuerteventura when the explosive was discovered, and everyone was apparently ordered back to a safe distance.
"It was obviously terrifying - the bomb could have been there for decades untouched but who knows what might have happened if it was disturbed," a set insider told Britain's The Sun newspaper.
"Some of the biggest stars in the world were on set and nobody was taking any chances. Fortunately, experts dealt with it."
It's believed that the bomb dates from World War Two, when the Nazis had a base on the island.
Angelina will star as Thena in the upcoming movie, while Richard takes on the role of Ikaris.
Speaking recently about the movie, Richard did his utmost to stay tight-lipped despite the GQ reporter's probing questions.
"I'm not really allowed to talk about it," teased Madden. "It's their new big superhero thing. I'm one of 10 immortals put on the planet... to, erm, protect us from bad guys." And when asked how it was meeting Jolie he answered: "She was just really lovely and wonderful and I'm really excited to work with her," before his publicist stepped in to cut him off.