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The fire led to one death and seven injuries.
The investigation involves two offices, the Supreme Procuratorate said: the Beijing People's Procuratorate and the district procuratorate of Chaoyang, the section of Beijing where the blaze at the China Central Television (CCTV) complex occurred.
The Supreme People's Procuratorate declined to elaborate on what the investigations covered.
China's procuratorate is the equivalent of a prosecutor's or attorney general's office, handling a range of civilian crimes, but it also has a special division responsible for crimes involving dereliction of official duty, such as bribery and corruption, that the police don't handle.
The fire, which engulfed the building that houses some CCTV facilities as well as the unopened Mandarin Oriental Hotel near the futuristic tower that will house the state broadcaster, was caused by a powerful fireworks show put on by CCTV.
One firefighter died from breathing toxic fumes and seven people were hospitalized. The huge blaze also caused widespread traffic congestion in eastern Beijing and led to the evacuation of hundreds of residents.
The police have detained 12 people so far, including a man in charge of the new site's construction, three CCTV workers and eight people CCTV hired from a fireworks company in central Hunan Province to stage the show.
The fireworks they used were dangerous and needed approval before being allowed in downtown Beijing, a Beijing government spokesman has said. He said that CCTV did not get approval and further alleged that its workers ignored police warnings that night.
Monday was the Lantern Festival, which officially ends the Lunar New Year, and it's traditional to light fireworks on that night.