The 20-year-old, who scored the goal which secured Palace's Championship survival in the 1-1 draw against Hull in 2011, links up again with his old Eagles team-mate and current Barnet boss Edgar Davids.
Sekajja is set to be included in the Bees squad to face Rotherham on Saturday.
He told the club website: "It is great to be here and it is great to link up with Edgar again because we had a good friendship at Palace.
"Coming on loan is a different challenge because you are playing against men but hopefully I can come in, play games and improve the team."
- Sports & Recreation