Law enforcement officials say a handful of men are under surveillance in New York City for ties to the chief suspect in a terrorist bomb plot.
Thus far, the only person that has been arrested is Najibullah Zazi, a 24-year-old Afghan man living in Denver.
However, investigators expect to make more arrests.
One official says those suspects are no longer considered a threat, because the plot was thoroughly disrupted.
Meanwhile, FBI Director Robert Mueller told a Senate homeland security hearing Wednesday that al Qaeda remains a serious threat.
"Al Qaeda has made a concerted effort to recruit Westerners -- they can fly under the radar passing through border controls," Mueller testified.
Michael Leiter of the National Counterterrorism Center said, "Al Qaeda remains intent on attacking on U.S. interests at home and abroad."
Just last week, federal agents made multiple arrests, disrupting three terror plots across the country.