Character mistake: When Andy and Barney are looking through the yearbook, Barny's middle name is Milton. But Barney says many times throughout the series that his name is Bernard P. Fife.
Character mistake: In the beginning where Karen is introduced to Andy and Barney in the coffee shop, her name is Karen Worth, then at the last where she is called as winner of the Skeet Shoot her name changes to Karen Moore.
Suggested correction: She is introduced as "Karen Moore". Thelma Lou's pronunciation is a bit off (what she says sounds like 'moor', as in an English moor), but she says "Moore."
Character mistake: Barney complains about Andy escorting the Apricot Queen around Mayberry many years prior. Barney had hoped to be her escort. He remembers the date, telling Andy it was "June 23, 1952, a Saturday afternoon." June 23, 1952, was a Monday.
Andy and the Gentleman Crook - S1-E21
Character mistake: When Barney and Gentleman Dan play gin, Barney deals only 8 cards. In gin, the proper amount would be 10.
The Arrest of the Fun Girls - S5-E28
Character mistake: Barney states when the Fun Girls were in town before, in Season 4, Thelma Lou didn't speak to him for 10 days. That's not true, they made up the same day.
A Black Day for Mayberry - S4-E7
Character mistake: When Opie comes in at the beginning of the episode and asks where Andy is, the exchange ends with Barney asking "Something you want to see him about?" and Opie replying "No, I'll wait," which makes no sense in context. It would have made more sense if Barney had asked "Do you want to leave him a message?"
Character mistake: When Barney walks by the barbershop window he glanced in and waves at Andy who is getting a manicure. But the man in the chair isn't Andy, it's a stand in. (00:17:00)
My Fair Ernest T. Bass - S4-E17
Character mistake: During the party at Mrs. Wiley's, Ernest Bass' girlfriend is called "Ramona." At the end of the show, Ernest T keeps calling her "Romina".