Asexual reproduction is the formation of new individuals from the cell(s) of a single parent. It is very common in plants but less common in animals. Asexual reproduction can occur however in some animals, and usually does so in a variety of ways depending on what type of species the animal is. Some animals may develop offspring by budding, whereas other animals may develop offspring by fragmenting into smaller pieces and maturing into a new animal. (worms are an example of fragmentation).
It is true that some frogs are in fact asexual beings. When the female organism lays eggs and they develop into an offspring without any fertilization it is known as parthenogenesis. This is how few fish, insects and even frogs are able to reproduce asexually.
There are a few disadvantages to asexual reproduction. One being that since the offspring is literally a clone of the parent, there is no difference at all and this can hinder the process of evolution. Another factor against asexuality is that these organisms that are asexual, reproduce this way because they are unable to adapt to their changing environments, which has brought a few species of animals close to extinction.