Still, Yellen remains fundamentally cautious, especially with a referendum on the U.K.'s European Union membership scheduled just one week after the FOMC's June 14-15 meeting.
"If they don't go in June and we have Brexit, or something else that prevents them from going in July, I don't think Janet Yellen is going to say, 'Darn, I should've taken the opportunity," RBS chief U.S. economist Michelle Girard told "Squawk Box."
"If I'm Janet Yellen, listen to what she said. She wants to be cautious. She wants to make a mistake of going too long. Let it run hot," she said.
Girard, who calls herself a hawk, said low rates have caused misallocation of resources, which has in turn restrained economic growth. The Fed would not be in a bind had it raised rates earlier, but the case for a rate hike is less compelling today than it was a year or two ago, she added.