"It was very mutual," says one insider.
The Fast & Furious 7 actress, 36, and Efron, 26, were first spotted kissing over the Fourth of July weekend during their vacation in Sardinia, Italy, with Italian entrepreneur Gianluca Vacchi. The flirty couple didn't keep much to themselves, documenting much of their romantic, PDA-filled fun on Instagram.
The pair were most recently seen in Ibiza, Spain, in early August, where they seemed to be enjoying each other's company on a date night.
"They seemed very close and comfortable together," an eyewitness told PEOPLE.
Prior to her romance with the Neighbors actor, Rodriguez was linked to supermodel Cara Delevingne, while Efron had a highly publicized breakup with longtime love Vanessa Hudgens in 2010.
Reps for the two have not yet commented.