The FA launched an investigation after Manchester City striker Bellamy shoved his hand into the face of a fan who invaded the Old Trafford pitch.
Neville, a non-playing Manchester United substitute, was also investigated for his actions in celebrating the home side's winning goal by running down the touchline towards the City fans. In the wake of Emmanuel Adebayor being charged with improper conduct for his inflammatory goal celebration last weekend, it had been predicted the FA might take action against the United full back.
But the FA have decided against charging either player with improper conduct, though referee Martin Atkinson told FA officials that he would not have sent off Bellamy had he seen the incident.
A statement released by the FA said: "The FA has today warned both Manchester City's Craig Bellamy and Manchester United's Gary Neville following separate incidents in Sunday's fixture at Old Trafford.
"In relation to Craig Bellamy the match referee has confirmed that he would not have sent the player off had he seen the incident with the fan at the time. Craig Bellamy will be contacted by the FA and warned as to his future conduct.
"The FA would repeat its previous advice that players should not become involved with or approach fans in such circumstances. The FA would also take this opportunity to remind fans, managers and players of their joint responsibility towards the game and strongly condemns any pitch invasions by fans. Gary Neville has been reminded of his responsibilities following his actions after Manchester United's final goal deep into injury time.''
United have also avoided any disciplinary action after City substitute Javier Garrido was struck on the head by a coin as he headed down the tunnel at half-time.
"The FA has also contacted Manchester United regarding a coin-throwing incident during the same fixture," the statement added. "The FA fully expects the club to use all available means to identify and deal with the culprit appropriately and, along with the fan who entered the field of play, look to issue bans on attending future matches."