Phonosemantic compound. 网 represents the meaning and 非 represents the sound. Based on the original meaning "fishing net". The current meaning is a phonetic loan.

Evolution

Seal script

Shuowen (~100 AD)

Clerical script

Western Han dynasty (202 BC-9 AD)

Clerical script

Western Han dynasty (202 BC-9 AD)

Clerical script

Eastern Han dynasty (25-220 AD)

Regular script

Modern