Mary Shelley's novel Frankenstein demonstrates the fear of the power of science in a couple different ways. First, Victor fails to realize his obsession with science has any power over him (this is recognized by the readers). Secondly, Victor's success at reanimating life leads to his own demise and loss of loved ones. This illustrates the idea that people should fear the power of science given it (science) is, essentially, the unknown.
Readers can see Victor's obsession with science as being a flaw (think Aristotle and hamartia (the tragic flaw of the tragic hero)). The fearful thing about this is that Victor, himself, fails to recognize the power of nature and how, when one interferes with nature, many things can go wrong. Essentially, science's power brings about fear because of its unknown qualities.
As for Victor's understanding of the power of science, and the fear associated with it, he does not realize how powerful science is until his success at reanimating life. Once his creature is "born," and Victor alienates it, the creature becomes far more powerful than Victor ever imagined. Instead, Victor honestly believed that he would be able to control his "son."
A new species would bless me as its creator and source; many happy and excellent natures would owe their being to me. No father could claim the gratitude of his child so completely as I should deserve theirs.
Therefore, as supported through Victor's own words, he believed that he could control nature. Unfortunately for Victor, he was very mistaken.
It uses the "ignorance is bliss" theme in a way, because the doctor works really hard to find out the secret of life, he achives it, and it brings him to his dawnfall. he loses his family, he loses his peace.