"I guess he looked really good," Mills said. "That's a neat thing to see. Everybody is hoping he can come back and throw the ball like he did in '09."
In 2009, Arias went 2-1 with a 3.35 ERA in 42 appearances, stranding 17 of 19 inherited baserunners. If he can return to this form, it would be a major boost for the bullpen.
Arias, who missed the 2010 regular season after undergoing right shoulder surgery, did not pitch in Spring Training and is currently on the 15-day disabled list, retroactive to March 22.
While Mills was encouraged by the reports from Arias' 60-pitch outing, he was reluctant to establish a timetable for the 27-year-old reliever's return.
"I'm going to have to go through his schedule," Mills said. "I haven't looked that far in advance."