The Bad Teacher actress was first said to be dating the professional baseball player in April 2010 and has been seen spending time with him in several public locations.
Last year, it was suggested that the couple had ended their relationship; however, they were later spotted holidaying in Mexico and have been seen together in a number of exotic destinations since.
Speaking to Elle, Diaz admitted that she and Rodriguez are an item.
"Yes, Alex is my boyfriend. It's not a secret anymore," she added.
Rodriguez was previously linked to Kate Hudson and Madonna, while Diaz formerly dated Justin Timberlake.
Watch the trailer for Bad Teacher below (warning: explicit content):