The couple, who originally began dating in 2010, were said to have split in May, though they later reunited in early June.
The Modern Family actress and Loeb are now planning to tie the knot, though no date for a ceremony has been set, reports US Weekly.
Vergara seemingly confirmed the report when she was pictured on friend Fernando Fiore's Twitter account wearing a diamond ring on her finger.
The wedding to Loeb will be Vergara's second. She was previously married as a teenager to Joe Gonzalez, with whom she has a 20-year-old son named Manolo.
Earlier this year, Vergara revealed that she would think about freezing her eggs in case she wanted to have more children in the future.