O'Flaherty, 29, is coming off Tommy John surgery. The left-hander went under the knife late last May and has been working his way back since. In eight minor-league rehab outings, O'Flaherty posted a 3.86 ERA, 0.96 WHIP and eight strikeouts in 9 1/3 innings. His last two outings for Triple-A Sacramento were scoreless.
The left-handed O'Flaherty was one of baseball's most dominant relievers before his injury for the Braves. From 2011-13, he had a 1.45 ERA, 1.09 WHIP and 124 strikeouts in 149 innings pitched.
O'Flaherty signed a two-year, $7 million deal with the A's this past offseason.