The US based Center for Inquiry said that she arrived in America last week.
It said she was "specifically named as an imminent target" by the same extremists who killed three secular bloggers this year in Bangladesh.
Ms Nasreen recently tweeted that she was not safe in India.
"Was threatened by Islamists who killed atheist bloggers in B'desh. Worried," she tweeted.
"Wanted to meet GOI (government of India) but no appointment. Left. Will be back when feel safe."
A strong critic of fundamentalist Islam, the 52-year-old feminist writer was forced to leave Bangladesh in 1994 after receiving death threats from radical Muslim groups who condemned a number of her writings as blasphemous.
She spent a decade in Europe and the US before India granted her a temporary residential permit in 2004.
The Center for Inquiry (CFI) in a statement said that it helped Ms Nasreen to move to the US in order "to alleviate the immediate threat to her life".
"Her safety is only temporary if she cannot remain in the US, which is why CFI has established an emergency fund to help with food, housing and the means for her to be safely settled," the statement said.
"Dr Nasreen arrived in Buffalo, New York on Wednesday and was met by CFI staff."
The CFI says that it has also heard from several other writers and activists in Bangladesh who have also been been named as murder targets because of their "secular advocacy".
Last month Bangladesh outlawed the Ansarullah Bangla Team (ABT) after a blogger - the the third to be murdered this year - was hacked to death. The ABT is the sixth Islamist militant group to be banned.
Police say that in each case, the attackers carried out their assaults on a busy street.
The first blogger to be killed - in February - was Bangladeshi-born US citizen Avijit Roy, who was killed in the capital, Dhaka.
In March blogger Washiqur Rahman was also hacked to death in Dhaka.
In May another blogger, Ananta Bijoy Das, was stabbed to death in the northern city of Sylhet.
A few years ago, hardline Islamists in Bangladesh demanded a blasphemy law to stop bloggers they perceived as being anti-Islamic from writing about Islam.
Bangladesh is officially a secular country but more than 90% of its 160 million population are Muslim.
Award-winning Bangladeshi writer and human rights activist Taslima Nasreen has fled from India to the US after she was named as an al-Qaeda murder target, a rights group has said.