The Centers for Disease Control and Prevention says that mosquitoes collected at 3 of 69 sites in January and February had genetic material indicating the presence of the virus.
Right now, scientists aren't certain if this means the West Nile virus will persist or pose a health hazard once warm weather arrives.
Correspondent Lou Young of CBS Station WCBS-TV reports, seven people died in the metropolitan area last summer, and dozens more were infected by the virus. The pathogen can cause encephalitis, a dangerous swelling of the brain.
People with weakened immune systems are at a higher risk. The West Nile symptoms resemble severe flu, with fever often accompanied by poor muscle control or mental disorientation.
The CDC said they would just have to wait and see whether the virus will persist and pose a threat this coming spring and summer, when mosquitoes are active.
"The bottom line here would be that we're not entirely certain what it means," said Dr. Stephen Ostroff, associate director of the CDC's National Center for Infectious Diseases.