A staff member opened a package delivered to the president's office Friday that contained a white powdery substance and a letter, and called authorities, said Secret Service spokesman Richard Staropoli. He described the letter as a "rambling diatribe."
Clinton was not at the office, in the upper Manhattan neighborhood of Harlem, at the time because he was attending events for his three-day birthday bash, a fundraising event for his foundation. His birthday was in August.
"The situation has not affected the president or Mrs. Clinton in any way whatsoever," Staropoli said.
Police and emergency crews were called to the office building around 3:45 p.m. Yellow police tape blocked off the sidewalk in front of the building, but traffic was not disrupted.
Clinton spokesman Jay Carson said the building was not evacuated. He had no other details.
Secret Service spokesman Eric Zahren said a field test on the substance found it to be inert.
Clinton signed a 10-year lease for the 8,300-square-foot penthouse floor of the 14-story building in 2001.
The city's Administration for Children's Services has a field office on four lower floors of the building.