Deepali ji,
Any deduction from salary is done from gross earning. Professional Tax is a deduction from your gross earning.
It seems you are from Mumbai. In Maharashtra, you are liable to pay Professional Tax: Nil If your gross earning is up to Rs. 5000/-p.m. Rs. 175/- if your gross earning is from Rs. 5001 to Rs. 10000/- and Rs. 200/- (or Rs. 300/- in Feb) if your gross earning is Rs. 10001/- and above.
I hope, you got the answer to your query.