The 34-year-old, who has 88 international caps for Mali, spent the last five months with Valencia in La Liga after moving from Chinese team Dalian Aerbin.
During his time with Los Che he made 11 league appearances, scoring one goal - the club's fastest ever in a match, coming after just nine seconds against Almeria.
Keita spent four years at Barcelona between 2008 and 2012, making 119 league appearances and scoring 16 goals, before joining Dalian Aerbin.
The midfielder started his career with Olympique de Marseille in Ligue 1 before moving on to Lorient and Racing Club de Lens, where he played over 200 times before joining Sevilla.
His contract with Roma will expire on June 30, 2015.