Luke Thompson, vice president of the Republican analytics firm Applecart, tweeted on Friday a screenshot of what he claimed to be Roberts' staff email address.
In the post, which has been retweeted more than 5,000 times, he said : "While you were having a nice Valentine's Day, @AOC decided to put her boyfriend on staff - drawing a salary on the taxpayer's dime. Nice to see her adapting to the swamp so quickly."
But Ocasio-Cortez said there was an innocent explanation.
In a reply to Thompson, she said Roberts has an email address so he can have access to her Google Calendar. "Congressional spouses get Gcal access all the time. Next time check your facts before you tweet nonsense," she said.
Ocasio-Cortez's Chief of Staff Saikat Chakrabarti also jumped to her defense.
"He's not paid. We have no volunteers in the office. He's not doing any government work. He can see her calendar just like spouses/partners/family members in other congressional office. Check your damn facts," he tweeted .