Facebook says they are removing "false claims" that fires in Oregon were started by certain groups, but Euronews has found examples of misinformation still circulating.
Deadly wildfires are continuing to rage across the US west coast, enveloping the skies above California, Oregon, and Washington in smoke.
At least 36 people have been killed, dozens more are missing, and whole neighbourhoods have been destroyed by the blazes.
The wildfires have divided opinion and campaigning ahead of November's Presidential election between Donald Trump and his Democrat rival Joe Biden.
And on social media, unfounded conspiracy theories have circulated the fires have been caused by the far-left political group, Antifa.
On Monday, police in Portland confirmed that one suspect had been arrested for starting seven small fires over two days. But no mention was made of the suspect's political affiliation.
The FBI bureau in Portland confirmed on Twitter that they had investigated claims that extremists are setting wildfires in Oregon and have found them to be "untrue".
"Conspiracy theories and misinformation take valuable resources away [from] local fire and police agencies working around the clock to bring these fires under control," FBI Portland said on Twitter.
One social media giant, Facebook, added that they are removing false claims that wildfires in Oregon have been started by "certain groups".
"This is consistent with our past efforts to remove content that could lead to imminent harm given the possible risk to human life," said Facebook's Head of Communications Andy Stone.
But an analysis by Euronews has found multiple memes and posts claiming that Antifa "extremists" have started the wildfires, some of which have received hundreds of likes and shares.
Other false claims say that Mexico and Canada have not been hit by wildfires. Official data from NASA shows that fires are however raging in many other countries besides the United States.