The Polish forces were leading an operation, alongside Afghan troops, to destroy a hidden explosives pile when the blast happened, the army said in a statement.
The death brings the number of Polish soldiers killed since the start of the war in 2001 to 42.
With 1,600 troops, Poland accounts for one of the larger contingents of NATO's International Security Assistance Force in Afghanistan. From October Poland is set to reduce the number to 1,000.
Poland would be limiting the presence of its troops overseas to concentrate on modernising its force, President Bronislaw Komorowski announced earlier this month.