There cannot be any positive level of output that a firm produce at which price is not equal to MC. Let us evaluate the following two cases where price is not equal to MC.
Case A: If P > MC
At output , Oq1 Price is Kq1, while the MC is Lq1. So, Oq1 is not the profit maximising output. This is due to the fact that the firm can increase its profit level by expanding its output to Oq2.
Case B: If P < MC
At output Oq3, price is Hq3 and MC is Gq3. So, Oq3 is not the profit maximising output.
This is because the firm can increase its profit by reducing its output level to Oq2.
Thus, at profit maximising point, price must be equal to MC and it cannot be greater or lesser than MC.