Will a magnet have an effect on an electric meter?

As Jim stated and sidelko stated, it can if you are adding one, as it can make the meter run backward or if the magnet is not strong enough, it can slow it down, therefore reducing your electric bill. As jim stated, this is highly illegal, it is considered grand larceny in many states. The reason many states consider it grand larceny is if they could not determine for sure the amount of energy you stole in a dollar amount. Many times they can figure it based upon previous usage and then get an average from that., By the way the significant change is usage is one of the things that the electric company first notices, because they have auditors who review accounts on either a monthly or quarterly basis. So if you know someone who is contemplating doing this, make sure that they are aware that they will eventually get caught, and depending on which state they live in, the penalties can be really severe. Here is what the penalties here in Texas are, just to give you a rough idea which depends upon how much the judge values the loss at (each state is different however).
Felony - 1st Degree - Fine up to $10,000 & or 5 to 99 years, 2nd Degree - Fine up to $10,000 & or 2 to 20 years, 3rd Degree - Fine up to $10,000 & or 2 to 10 years.
Hope this better explains it. Susu