Roberts, who is dating actor Garrett Hedlund, posted three photos on Instagram on Monday.
The 29-year-old hinted that she is expecting a boy with the caption: "Me... and my two favourite guys."
In the first photo, she is seen sitting and cradling her baby bump, while Hedlund, 35, is seen with her in the second and third photos.
Roberts was congratulated by several celebrities, including her famous aunt, Oscar-winning actress Julia Roberts, who wrote "Love you" with a kiss emoji.
Glee star Lea Michele, who just gave birth to a baby boy last month and was Emma Roberts' co-star in television series Scream Queens, wrote: "You will be the greatest mama. I love you Em. Boy moms together."
Entertainment magazine Us Weekly first reported that Roberts was pregnant with her first child in June.
Her mother Kelly Cunningham seemed to have confirmed the news then, when she was asked by a netizen on Instagram, but her account was later deactivated.
Roberts, who was in the TV series American Horror Story and the movie Scream 4, was linked to Hedlund in March last year after a seven-year on-off relationship with her American Horror Story co-star Evan Peters.
Hedlund previously dated actress Kirsten Dunst for four years before they broke up in 2016. – The Straits Times/Asia News Network
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