The poll showed that 68 percent of the people interviewed thought that IS posed a very serious threat, compared with just 39 percent who thought so about Iran, 32 percent about North Korea, and 25 percent about Russia, Xinhua reported on Wednesday.
Nearly nine in 10 people saw the IS as, at least, a moderately serious threat.
People across political and ideological lines, including 68 percent of Democrats, 79 percent of Republicans and 63 percent of independents felt that the IS was a deep and serious threat to the US.
Last Sunday, six Somali-Americans from the state of Minnesota were arrested by US Federal Bureau of Investigation (FBI) for trying to join the IS, raising concerns that the threat posed by the group was growing and the battle against the IS could spread.
In a CNN/ORC poll last month, the public remained mostly confident that the US effort to combat the IS would succeed.
It also showed that 79 percent of the Americans were worried that the conflict would develop into a larger war that would spread to other parts of the world.