The 34-year-old has become a key part of the Giallorossi's midfield since joining the club in the summer after six months at Valencia.
"As you know, after my return from China the six months at Valencia allowed me to prove my ability to return to the top level, to show I had lost none of my skills," he told malifootball.com.
"Therefore I signed for Roma. Valencia really did want me, but I wanted to play at the highest level, especially the Champions League.
"This is the best team I've found and it is my ambition to show I can be part of the best."
Keita has scored 23 goals for Mali in 90 appearances for the national side.