A Bidhannagar sub-divisional court magistrate convicted and sentenced Sen to three years' rigorous imprisonment and a fine of Rs 10,000.
Sen, whose Saradha Group ran the ponzi schemes under different names, would have to undergo another six months' imprisonment if the fine is not paid, the court directed.
He was convicted under section 406 (criminal breach of trust) for default in depositing provident fund (PF) of employees, to which Sen confessed before the court.
He was also sentenced to three years' imprisonment for 'conspiracy' under section 120B of IPC in connection with the PF default.
Both the terms would continue concurrently and the number of days he has already undergone imprisonment since his arrest in April, 2013 would be deducted from his imprisonment term.
Several hundred cases are still pending against Sen, accused of duping lakhs of depositors in West Bengal and other states.