U.S. Sen. Dianne Feinstein, D-Calif., made the remark as she opened a hearing on national security threats against the United States.
Feinstein said there had been no terrorist attacks on U.S. soil since the committee's most recent threat hearing although "numerous plots against United States interests overseas have been prevented."
"I'm concerned that this success has led to a popular misconception that the threat has diminished," Feinstein said. "It has not."
In fact, she said, "terrorism is at an all-time high worldwide."
"If you include attacks by groups like the Taliban against the United States military and our coalition forces, according to the [National] Consortium for the Study of Terrorism and Response to Terrorism, at the University of Maryland, which is the source for the State Department's official tallies, there were more than 8,400 terrorist attacks, killing 15,400 people in 2012," Feinstein said.
"The instability that spread through North Africa and the Middle East during the Arab Spring has continued to lead to an increase in the terrorist presence and terrorist safe havens throughout the region," she said.
"But I think the most notable development since last year's hearing is actually in Syria, which has become a magnet for foreign fighters and for terrorist activity."
Feinstein said the regime of Syrian President Bashar Assad cannot control the situation, leading to concern terrorists have established a safe haven in Syria "and the real prospect that Syria could become a launching point or way station for terrorists seeking to attack the United States or other nations."
Director of National Intelligence James Clapper, testifying before the committee, said he has "not experienced a time when we've been beset by more crises and threats around the globe."
He called on former National Security Agency contractor Edward Snowden "and his accomplices" to return stolen national security documents that have not yet been made public.
Clapper said Snowden's disclosures have caused "profound damage" to U.S. security.
"What Snowden has stolen and exposed has gone way, way beyond his professed concerns with so-called domestic surveillance programs," Clapper said. "As a result, we've lost critical foreign intelligence collection sources, including some shared with us by valued partners.
"Terrorists and other adversaries of this country are going to school on U.S. intelligence sources' methods and trade craft and the insights that they are gaining are making our job much, much harder."