It is still unclear whether Obama was in the office when the questionable mail arrived.
Mr Obama has leased offices in the building since he left the White House in 2017.
The building - the headquarters of owners World Wildlife Fund (WWF) - has been cordoned off and the area is on lockdown until police give the all clear.
The suspicious package was reported at approximately 12:30 pm and was delivered in a letter marked as having come from Hong Kong. Mr Obama lives with his family in the nearby Kalorama neighbourhood. The white substance turned out to be cornstarch.
There is no indication if Obama was at the office at the time the package was discovered.
Vanessa Trump was rushed to the hospital after she opened the letter and found the white powder.
Both incidences have recalled the scary days after 9/11 when letters containing lethal anthrax spores were sent to the offices of several politicians and media outlets - resulting in five deaths.
This comes just a day after Donald Trump's daughter-in-law Vanessa Trump was sent to hospital after a letter containing a similar "suspicious substance" was sent to her apartment in NY.
The NYPD also said that the Secret Service would also be a part of the investigation.