Fear of God is righteous. Fear of things which are dangerous is intelligent.
Fear imo is only a sin when it prevents us from doing that which God requires us to do. When it hinders us from following Him. Irrational fears, fears which consume us or hold us back, fears that we hold onto when God tells us to let them go, those to me are sin. There's no Bible verse saying "Fear is a sin." There a many Bible verses of God helping us and guiding us through our fear, but that doesn't make it a sin.
"To everything there is a season,
and a time to every purpose under the heaven"