Assistant superintendent Musa Magaji Majia said Hassan Zein was discovered unharmed, dumped on the outskirts of Kano on Friday.
Zein was seized Monday by armed men who stormed the compound of his factory, M.C. Plastic Co.
His family said no ransom was ever demanded or paid, though they usually are for kidnappings in Nigeria. Majiya also insisted no ransom was paid.
Majiya said nobody has been arrested in the case by police are continuing investigations.