Felons typically do not have a right to vote. In fact, it's estimated that 5.85 million people have been barred from voting in elections, according to FelonVoting.org. This is due to a process called disenfranchisement. Not all states are the same, with Vermont and Maine allowing people with felony convictions to vote while they're in prison.
There are at least nine other states that permanently ban certain kinds of felons from voting. It's argued, of course, that once the people have paid their dues, they should have their voting rights reestablished. Otherwise, it could be seen as unfair and undemocratic.