"I am shocked that Twitter has not taken down his tweet because he's threatening her life," Hostin said on Thursday.
The post, which Trump retweeted on Wednesday, appeared to be removed, although it's unclear when.
It showed Omar dancing during a Congressional Black Caucus event that occurred on Sept. 13, two days after the 18th anniversary of the attacks on 9/11.
Hostin's comments echoed a tweet from Omar accusing Trump of spreading lies and risking her life.
"This is from a CBC event we hosted this weekend to celebrate black women in Congress. The President of the United States is continuing to spread lies that put my life at risk. What is Twitter doing to combat this misinformation?" she asked.
Co-host Joy Behar noted that former President Barack Obama advised against presidents watching television and going on social media.
"That's Obama, who we miss very much," Behar commented.