A much-travelled Kharja, who scored 12 goals in 75 internationals, was a free agent after leaving French club Sochaux in the summer.
The 32-year-old enjoyed a successful career in Italy with several clubs including Inter Milan, AS Roma and Fiorentina, before accepting a lucrative offer from Qatari club Al-Arabi in 2012.
"Steaua are a team with a glorious history and impressive performances in Europe," Kharja said after passing a medical in Bucharest on Friday. "They're the champions of Romania and I am excited."
The 26-times Romanian champions Steaua, the 1986 European Cup winners, are fifth in the Romanian league with 16 points from 10 games, four points behind leaders FC Astra.
"Of course, we have the chance to win the championship, it's still early in the season," Kharja said. "We're a only a few points behind Astra and I hope we'll manage to cut the difference."
By signing Kharja, Steaua hope to finally fill the void left by highly-rated midfielder Lucian Sanmartean, who agreed a one-year deal with Saudi Arabia's Al Ittihad in January.
(Reporting by Angel Krasimirov; editing by Amlan Chakraborty)
