The writer, Katie Rich, during Trump's inauguration on Friday, sent out a tweet that mocked Barron Trump, who is 10 years old. The tweet was widely criticized by many on social media.
The backlash went as far as an online petition that called for NBC to fire Rich. That petition has so far accumulated more than 85,000 signatures on Change.org.
Rich deleted the tweet as well as her Twitter account, which she then reactivated on Monday in order to post an apology.
"I sincerely apologize for the insensitive tweet, I deeply regret my actions & offensive words. It was inexcusable & I'm so sorry."