"It's early in the season. We're down about 5 percent," said Roberts. "That's a lot lower [decline] than people originally thought."
Comcast airs NFL games on its NBC network Sunday nights and Thursday nights. NBC also has the Super Bowl this year.
Each year gets more difficult for traditional media players to grow audiences as new platforms emerge, Roberts said.
"There are a lot more choices," he noted. "The world has changed, and so does the NFL. And they'll have to look at their own business."
According to an ESPN report, citing metrics from Nielsen, total viewership has fallen about 7.5 percent to an average of 15 million people through the first six weeks of the NFL season.
President Donald Trump has claimed the NFL ratings decline is due to the controversy of players kneeling during the national anthem. The president has repeatedly criticized the protests, and said owners should fire players who don't stand.
The anthem firestorm started last season when then-San Francisco 49ers quarterback Colin Kaepernick took a knee during the anthem to protest the treatment of African-Americans in the United States.
Despite the ratings declines, Roberts said the NFL has demonstrated it is "the best in sports at what they do" in delivering a quality experience to fans.
Disclosure: Comcast owns NBCUniversal, the parent company of CNBC and CNBC.com.