The company had to offer standalone Internet for $49.95 for three years and had to “visibly offer and actively market” the option.
But the FCC's investigators accused Comcast of not doing enough to promote the standalone Internet service.
FCC Enforcement Bureau Chief Michele Ellison said the settlement "sends a clear message" that the FCC will "vigorously enforce its merger conditions."
It is the first time the FCC has forced a company to extend a condition of a merger.
Sena Fitzmaurice, a spokeswoman for Comcast, said the company has incorporated the commitments and conditions of its NBC merger into the "DNA of our business practices."
"We are proud of our standalone broadband offering of ‘Performance Starter’ service — we rolled this product out in just one month, the fastest Comcast has ever deployed a brand new service simultaneously throughout its footprint," she said in a statement.
She said the FCC had questions about whether the company could have done a better job rolling out the service.
"We are pleased that Comcast and the FCC were able to address such issues cooperatively and constructively in a consensual manner," she said. "We look forward to continuing to offer and market Performance Starter in additional ways and with additional outlets."