The Ninja Jaffa were a special class of Jaffa among Anubis's forces and served as his personal guard. They were few in numbers but made up for it in skill. A group of Ninja Jaffa was always present with Anubis after his return. These Jaffa do not wear traditional Jaffa armor but ninja robes and cloaks; they also possess swords.
When SG-1 found Anubis' Ha'tak in orbit over Earth, they inadvertently freed a group of Ninja Jaffa by opening a sealed compartment. The Jaffa proceeded to kill Dr. Friesen and injure Jacob Carter before being stopped by Teal'c and Jonas Quinn. (SG1: "Descent")
When Anubis attacked Abydos, two Ninja Jaffa were present when Her'ak was negotiating with Colonel Jack O'Neill. When Anubis attacked Kelowna, two Ninja Jaffa were present with Anubis at all times. (SG1: "Full Circle", "Fallen", "Homecoming")