"So ridiculous. Donald must work on his Anger Management problem, then go to a good old fashioned movie with a friend! Chill Donald, Chill!"
Her comment is a jibe at Trump after he mocked her on social media after she was named Time Magazine's Person of the Year in 2019.
At the time, he tweeted she should "work on her anger management problem, then go to a good old fashioned movie with a friend".
It's not the first time Thunberg has weighed in on the election debate.
The Swede made a rare comment four weeks ago, saying she never engages in party politics but "the upcoming US elections is above and beyond all that".
In her tweet, she encouraged Americans to vote for Biden.
"From a climate perspective it's very far from enough and many of you of course supported other candidates. But, I mean you know, damn! Just get organised and get everyone to vote Biden."
While Thunberg has endorsed Biden, she has recently scoffed at both candidates' environmental plans and efforts to help solve the climate crisis.
In an interview with the New York Times, Thunberg was scathing in her assessment of the US election and the environmental policies on offer from Biden and Trump.
She said: "Maybe if Trump wins that will be the spark that makes people angry enough to start protesting and really demanding things for the climate crisis.
"I think we can safely say that if Trump wins it would threaten many things.
"But I'm not saying that Joe Biden is good or his policies are close to being enough. They are not."
