The higher orange alert lasted 10 days. No domestic terrorist strikes were attempted during that period.
"The intelligence community has concluded the number of indicators and warnings that led to raising the threat level have decreased, and the heightened vulnerability associated with the Memorial Day holiday has passed," said Brian Roehrkasse, spokesman for the Department of Homeland Security.
Level orange indicates a high risk of terrorist attack, while yellow is elevated. It's the middle level on a five-color scale. The lowest two levels, green and blue, and the highest, red, have not been used since the system was adopted in March 2002.
"It's not so much what has happened as what's has not happened," says CBS News Correspondent Jim Stewart. "I don't sense that their apprehension has dropped, but certainly their sense that anything imminent is about to happen is dropping."
The alert level was raised on May 20 after terrorists believed linked to al Qaeda struck in Saudi Arabia and Morocco. Seventy-five people were killed, including eight Americans.
Homeland Security Secretary Tom Ridge said it was feared the incidents could mark the beginning of a wave of worldwide attacks that could include U.S. targets.
With the alert, government authorities and businesses stepped up security, particularly at large gatherings over the Memorial Day weekend. Lowering the alert level would allow authorities to scale back some security measures, a move favored by many local governments struggling with budget shortfalls.
"It costs a great deal of money to pay overtime to police officers. It costs a great deal of money to keep aircraft over New York and Washington," said Stewart. "At one point during the Iraqi war when we were at Condition Orange, there was an estimate that it was costing us as much as $2 billion to keep the nation at that high an alert level."
The terror alert has been at orange four times since the system was put in place. No domestic attacks have occurred during any of the alerts, which Homeland Security officials believe serve to deter would-be terrorists from striking.
Previous alerts lasted roughly a month.
U.S. officials suspect al Qaeda's top leaders coordinated the Morocco and Saudi Arabia attacks to demonstrate al Qaeda still is viable.
Many of those leaders are believed to be in Iran, although Osama bin Laden is thought to be in the remote border region between Afghanistan and Pakistan. Their activities, along with information gleaned from prisoner interrogations and intercepted communications, played a key role in raising the alert, U.S. counterterrorism officials said.
Stewart doesn't expect the terror alert level to go below yellow any time soon.
"We'll probably never see green," he said. "I doubt that we'll ever get out of this yellow or elevated sense of alert for some time, as long as there are questions out there about al Qaeda's capabilities, and certainly late they've shown they still have some."