Baha'i Beliefs about Evil
The Bahá'í Faith rejects the concept of "original sin" or any doctrine that teaches people are basically evil or have intrinsically evil elements in their nature. All the forces and faculties within us are God-given and thus potentially beneficial to our spiritual development.
However, if a person, through his own God-given free will, turns away from this force or fails to make the necessary effort to develop his spiritual capacities, the result is imperfection. `Abdu'l-Bahá said that "evil is imperfection."
The Bahá'í Faith denies the existence of Satan, a devil, or an "evil force." Evil does not have independent existence, but is rather the absence of good, just as darkness is the absence of light and cold is the absence of heat. Just as the sun is the unique source of all life in a solar system, so ultimately is there only one force or power in the universe, the force we call God.
Bahá'u'lláh explained that references to Satan in the Scriptures of earlier religions are symbolic and should not be taken literally. Satan is the personification of man's lower nature which can destroy him if it is not brought into harmony with his spiritual nature. There is, in fact, a well-known philosophical problem concerning God's goodness and omnipotence and the possible existence of a Satan. This problem is discussed in some detail in both the writings of Bahá'u'lláh and `Abdu'l-Bahá.
More - On Good and Evil - Bahai.org