There were no details about the scope of the deployment but the state's Defense Minister was to give a press conference on Tuesday.
The defense ministry announced late Monday that "from this moment, the defense ministry is mobilizing troops" in Brazil's second biggest city.
There were no details about the scope of the deployment but Defense Minister Raul Jungmann was to give a press conference Tuesday.
The decision to send in the army comes as relatives of police officers in Rio continued to attempt to blockade several stations in protest at conditions and late payment of salaries.
Street police are barred by the constitution from demonstrating.
However, the tactic of relatives camping outside stations to paralyze the officers' movements has recently been employed across Espiritu Santo state to the north of Rio, sparking a complete breakdown in law and order.
The protest movement was on a much smaller scale in Rio, but several bases, including the headquarters of the elite Shock Battalion riot police, have been partially shut down for days. Police officials acknowledge that morale is low but have warned officers not to strike.
An insufficient number of police was widely blamed for violence at a Botafogo-Flamengo football match on Sunday in Rio where one person was shot dead and seven others were injured.
Rio de Janeiro is also on edge after violent crackdowns over the last two weeks by riot police against demonstrators protesting the planned privatization of the state water utility. More protests were expected this week.
Adding to the security challenge, February is carnival season and big street parties take place every day, building up to parades by the city's top rival samba schools on February 26-27.
Troops are frequently used in Brazil to augment the frequently stretched police or to quell crime waves.
They were sent into Espiritu Santo to replace the striking police and have also been deployed in large numbers in Rio for recent legislative elections and during the 2016 Olympics.