Johnson was found guilty of sexual touching but cleared of one charge relating to another sexual act following a trial at Bradford Crown Court.
The court was told the grounds for appeal had been lodged on Thursday.
The former Sunderland winger is in court awaiting sentencing.
Johnson previously admitted grooming the girl and one charge of sexual activity.
Judge Jonathan Rose previously warned him he faced a "substantial prison sentence".
Ex-England footballer Adam Johnson is to appeal against his conviction of sexual activity with a 15-year-old girl.