The 39-year-old, who is currently filming Thor: Love and Thunder in Australia, was pictured out and about in the city on Saturday.
On Friday, the actor shared a screengrab of the article on her Instagram Story and confirmed that she was not, in fact, pregnant.
“Hey, so I’m totally not pregnant,” she wrote.
“But apparently it’s still okay in 2021 for anyone to speculate and comment on a woman’s body shape whenever they want? Do better.”
Portman already has two children with husband Benjamin Millepied, who she met while filming Black Swan in 2009 before marrying three years later.
The couple welcomed their son, Aleph, in 2011, and their daughter, Amalia, in 2017.
On Instagram, Portman shared a lengthy message about her mother, describing her as “the most loving, caring, generous, cuddly, funny, smart, talented, creative person I could ever imagine getting to spend my childhood with”.
In a second post, the Jackie actor shared a throwback picture of herself cuddling her two children.
Portman captioned the image with a series of love heart emojis.