Given that the theme of justice and injustice is highlighted in Mary Shelley's Frankenstein, readers can only expect to find examples of both existing within the text.
During the trial of Justine, Elizabeth comes to her defense denying that Justine could have ever murdered William (showing her choice to be just--do what is right). That said, Victor knows who committed the murder and fails to stand up for Justine. Through his alienation of her, Victor shows himself, and his actions, to be unjust. In the end, Justine is hanged for a murder she did not commit (a true showing of injustice).
Creation of the Creature
While some may argue that Victor's creation of the Creature could not be deemed just or unjust, when examining it from a genetic side, one can only state that Victor is acting unjustly towards women. Given that, to this point, women were the only ones who could "birth" or give life to another human being, Victor has taken this away from them. He has treated women unjustly, overtly, by taking the one thing away from women they possessed over men.
Victor, The Judge and Jury
Lastly, Victor consistently acts as both judge and jury throughout the novel. While all others in the novel are open to hearing what others have to say, Victor consistently shuts out all others around him. Compounding his "God-Complex," Victor fails to openly and fairly take into consideration the feelings of those around him (most importantly, the creature).