Why are "Fear and Shame" listed among the beautiful cetasikas? I was wondering how the mental factors of Fear and Shame should be understood. Normally I would understand them both as being unwholesome but I guess in Abhidhamma-perspective they have a different meaning. 

How should they be understood according to the Abhidhamma?

They are both listed as belonging to the group of Beautiful or Moral cetasikas.
It's a translation issue. The Pali terms are Hiri and Ottappa, and they are hard to translate into English because they have no one word equivalents.

Hiri refers to the feeling of not wanting to do a bad deed because you know the deed itself is bad, and Ottappa refers to the feeling of not wanting to do an evil deed because you know that the consequences of it are bad.

They definately do not mean what is normally meant by the English words fear and shame. Many suttas speak of fear as unwholesome, and shame in the sense of remorse is mentioned as unwholesome in other Buddhist writings.

For this reason the translator Ajahn Thanissaro prefers to translate these terms as conscience and concern.

The Ven. Bhikkhu Bodhi wrote a very good article on these two terms called The Guardians of the World. Here's a very good excerpt:


  While moral shame and fear of wrongdoing are united in the common task
  of protecting the mind from moral defilement, they differ in their
  individual characteristics and modes of operation. Hiri, the sense of
  shame, has an internal reference; it is rooted in self-respect and
  induces us to shrink from wrongdoing out of a feeling of personal
  honor. Ottappa, fear of wrongdoing, has an external orientation. It is
  the voice of conscience that warns us of the dire consequences of
  moral transgression: blame and punishment by others, the painful
  kammic results of evil deeds, the impediment to our desire for
  liberation from suffering. Acariya Buddhaghosa illustrates the
  difference between the two with the simile of an iron rod smeared with
  excrement at one end and heated to a glow at the other end: hiri is
  like one's disgust at grabbing the rod in the place where it is
  smeared with excrement, ottappa is like one's fear of grabbing it in
  the place where it is red hot.


http://www.accesstoinsight.org/lib/authors/bodhi/bps-essay_23.html