The 34-year-old actor, who also starred in the recently cancelled NBC comedy 'The New Normal', popped the question to his fitness-trainer girlfriend while they were vacationing in Big Sur this month, reported Us magazine.
"Bartha proposed at the Post Ranch Inn with an unbelievable engagement ring," a source said.
The actor's representative is yet to confirm the news.
Bartha and Smith met during a Pilates session at an LA gym where Smith works as an instructor. They debuted their romance this January while vacationing in Maui.
This would be the actor's first marriage. He was previously linked to actress-turned-designer Ashley Olsen for two years. They broke up in March 2011.