2 Corinthians 3:7But if the ministration of death, written and engraven in stones, was glorious, so that the children of Israel could not stedfastly behold the face of Moses for the glory of his countenance; which glory was to be done away:
(2 Cor. 3:7 KJV)
The people were afraid to come near Moses perhaps because the glory of his face show forth the holiness of God. Indeed, the people has just been delivered from the fierce bout of idolatry. There is a sense of awe even though they have repented of their sins.

We are reminded of the scene of the giving of the Ten Commandments in Exodus 20 and the fear of the people in the awful sight of thunderings and lightnings that caused them to be afraid. Moses drew near unto the thick darkness where God was. There is a sense of a fearsome power emanated from the presence of God.