Miller announced her return in a tweet which said she has since had three negative tests for Covid-19.
Miller also revealed in the tweet that she was pregnant. She credited her husband, Stephen Miller, a senior advisor to President Donald Trump, with having taken "great care" of her during her time away from the job.
She had disclosed on May 8 that she tested positive for the coronavirus. The announcement came a day after news broke that a personal valet for Trump had tested positive for the virus.
Several days after Miller and the valet tested positive, White House staffers were told that they had to wear masks when they entered the West Wing of that building, which contains the Oval Office where the president works.
The memo also asked staff members to avoid visiting the West Wing unless it is necessary.
Despite the precautions, Trump has refused to wear wearing masks in public settings, even as federal health guidance urges all Americans to do so when unable to maintain a 6-foot distance from others.