"They're just going away for a few days to relax," says a source.
The group plan to stay at Gibson's Costa Rican home. They will be back early next week.
The unlikely pair were first spotted together back in mid-March when they dined at Russian restaurant Romanov in Studio City. However, it wasn't their first meeting. Gibson and Spears and their families met a number of times after the pop star was hospitalized in February, a different source told PEOPLE at the time.
"Mel and his wife Robin clearly saw a woman in crisis and wanted to extend themselves in any way possible," the source said.
Gibson and Spears used to be neighbors when the singer previously lived in Malibu. "There are no expectations, there is no agenda," the source added. "It's simply an act of human kindness – one neighbor reaching out to the other."