Three army vehicles carrying dozens of soldiers drove down Qasr al-Nil Bridge early Friday evening.
They were seen heading toward the headquarters of Egyptian State TV on Corniche al-Nil.
The area also houses the ruling National Democratic Party headquarters and the Ministry of Foreign Affairs.
The Egyptian Army were previously twice deployed in Cairo in 1977 during bread riots and in 1986 to quell police riots.
During the last six decades, the army has never fired on Egyptian civilians.
