The find was made in the coastal city of Ashdod by a team of researchers from Tel Aviv University and Leipzig University.
The ancient city of Ashdod-Yam was in the southern part of the modern city and was one of the most important areas of Israel in the Byzantine period.
This is the third season of excavations being held in the region, and footage of the dig has been released by the Israel Antiquities Authority (IAA).
The inscription uncovered on the mosaic reads: ‘By the grace of God (or Jesus), this work was done from the foundation under Procopius, our most saintly and most holy bishop, in the month Dios of the 3rd indiction, year 292.’
Dr Leah Di Segni, of the Hebrew University of Jerusalem, said: ‘This is the earliest appearance of the use of the Georgian counted in Israel, many years before it is used in Georgia itself.’