Arguello, a 33-year-old civil and architectural engineer, and Longoria are said to be staying together at her Los Angeles pad, reported TMZ.
"Eva and Ernesto have been hitting the town together too, hitting up Chateau Marmont on the Sunset Strip on Sunday night, and the exclusive Soho House on Monday," a source said.
Despite the reports, Longoria, 38, is adamant that they are just friends and had tweeted yesterday, "Sorry Ernesto Arguello is not dating me."