Goodell said on the Dan Patrick radio show the key issue is a "pattern of behavior" and "bad judgments."
Last week, prosecutors in Georgia declined to charge Roethlisberger after a college student accused him of sexual assault in March.
The NFL is expected to discipline Roethlisberger, although it says there is no timetable for such a decision. The Steelers have said they expect a decision next week.
Roethlisberger also is being sued by a different woman who says he raped her in 2008 at a Lake Tahoe hotel-casino. Roethlisberger denies the accusation and was not charged. He has claimed counter-damages in a lawsuit.
"The issue here is with respect to a pattern of behavior and bad judgments," Goodell said. "You do not have to be convicted or even charged with a crime to be able to demonstrate that you've violated a personal-conduct policy, and reflect poorly not only on themselves, but all of their teammates, every NFL player in the league, and everyone associated with the NFL. That is what my concern is, and I have expressed that directly to Ben, obviously, and I'll be making a decision as soon as I possibly can."
Meanwhile, Roethlisberger practiced Monday with the Steelers, with several players saying they were warned that misconduct will not be tolerated. One added they were told to "get in line" or "get kicked out of line."
The quarterback did not speak to reporters after practice.
At a meeting with coach Mike Tomlin before practice, multiple players said they were told the Steelers now have a zero-tolerance policy regarding misconduct. Wide receiverfor a fifth-round draft pick last week following a series of problems.
"We were told early this morning that either you get in line or you'll get kicked out of line - you're going to be traded or you're not going to be here," right tackle Willie Colon said. "If your conduct is going to play a part in you not being a good football player, they're going to get rid of you."
Tomlin met with players before practice and that's where players said the message was delivered. The coach, however, denied making those remarks. Tomlin rarely discusses issues he addresses with his players.
"Guys took it different ways, depending on how they interpreted it, but I think ... after what we've seen go on, there's not going to be much tolerance for stuff around here," Smith said.
This was a voluntary practice for the Steelers, their first since they concluded a 9-7 season in January. Roethlisberger also participated in off-the-field conditioning work for several days last week.
The quarterback had been accused by a college student of sexual assault in March. Team president Art Rooney II said the Steelers were ready to punish the quarterback, but declined to do so because such action could be contested by the players' union.