Mathis was placed on the PUP list at the start of training camp as he continued his rehabilitation from a torn Achilles suffered in September 2014.
"It felt awesome," Mathis said after practice. "It's been a long time. Felt like a rookie again. Had butterflies, nervous. It was definitely worth it. The toughest part was waiting. Just taking it one day at a time. Doing the little things and just happy to get out there."
Mathis said in June that his goal is to be on the field with his teammates for their Week 1 game at the Buffalo Bills. It's uncertain whether that will happen; Colts owner Jim Irsay said earlier this month that it could be late September or early October before Mathis plays.
Coach Chuck Pagano said the Colts will take a cautious approach with Mathis regarding when he'll play in the regular season. When asked whether he plans to play at Buffalo, Mathis said "Yes." But he later softened his words.
"As an athlete, you give yourself a timeline," he said. "You work hard to meet your own personal deadline. When they're ready for me, they're ready for me. I can't control that. I just bump my hump, be ready. So when my number is called I'll be ready."
Mathis led the NFL in sacks (19.5) in 2013. He was suspended for the first four games of last season for using performance-enhancing drugs. The torn Achilles ended any possibility of him playing last season.