The five-meter (around 16-feet) high pyramid was found 20 meters beneath the sands at Saqqara, a short distance from the world's oldest pyramid. It is the 118th pyramid to have been discovered in Egypt.
The discovery was made two months ago, but was announced on Tuesday at Saqqara, some 19 kilometers (12 miles) from the capital, Cairo.
The pyramid is believed to date from the reign of Queen Seshseshet, mother of the King Teti I of ancient Egypt's Sixth Dynasty (2323-2291 BC), the country's antiquities chief, Zahi Hawass, said.
"This is one of the most significant discoveries in recent years," Hawass said, adding that the pyramid was originally about 14 meters high.
Archaeologists earlier discovered a papyrus written by Queen Seshseshet in which she asked Egyptian medics to help her treat her hair.
Hawass said his team of archaeologists would continue their excavations at Saqqara, saying: "The Egyptian sands contain many more mysteries."