The limestone artefact, believed to be a stylized representation of an ancient Roman emperor, was found inside a two-level tomb near the temple in southern Egypt, the ministry said in a statement.
Next to the "beautifully and accurately carved" sphinx, researchers had found "a Roman stele written in demotic and hieroglyphic" scripts, the ministry's statement said.
Once fully deciphered, the stele may shed light on the identity of the sculpted ruler, who the Egyptian research team said could be Emperor Claudius.
Hathor Temple, about 500 kilometers south of the capital Cairo, was home to the Dendera Zodiac, a celestial map which has been displayed at the Louvre in Paris since 1922, more than a century after Frenchman Sebastien Louis Saulnier had blasted it out of the temple.
Egypt wants it back.
The country has unveiled major archaeological discoveries in recent months, primarily in the Saqqara necropolis south of Cairo but also in Giza, home of the only surviving structure of the seven wonders of the ancient world.
On Thursday, the antiquities ministry announced the discovery of a hidden nine-meter passage inside the Great Pyramid of Giza, which archaeologist Zahi Hawass said may lead to "the actual burial chamber" of pharaoh Khufu, or Cheops.
Further south, in Luxor, archaeologists had discovered an 1,800-year-old "complete residential city from the Roman era", authorities announced in January.
Some experts see such announcements as having more political and economic weight, than scientific, as Egypt is counting on tourism to revive its vital tourism industry amid a severe economic crisis.
The government aims to draw in 30 million tourists a year by 2028, up from 13 million before the pandemic.