1. A method for preventing an error in a physically unclonable function (PUF), comprising: selecting any value, from a physically unclonable function based on a volatile memory device, as an input value, and checking a response corresponding to the selected input value; classifying cells having a plurality of bits corresponding to the response depending on frequency of error occurrence; calculating a number of white cells, in which an error does not occur, from classified results; and determining whether the number of white cells is greater than a preset threshold number of white cells, and selecting an input value of the physically unclonable function based on results of determination.