In an electric circuit, if the flow of electrons is from negative to postive, then why do the current flows from positive to negative
The direction of flow of electrons in a circuit is opposite to the direction of the flow of current. Protons of an atom don’t take part in conduction of electricity.
Accumulation of electrons in the negative terminal of a battery creates a negative potential (low potential), and the deficiency of electrons in the positive terminal creates a positive potential (high potential). Hence, electrons flow from low potential to high potential; but current as we know flows from high to low potential.
Flow of current is not the flow of positive charge or protons. It is a convention that has been followed since the discovery of electric charge, that current flows from high potential to low potential.