The FA had looked at an incident where Shelvey made a swimming gesture toward home fans at the Cardiff City Stadium.
The gesture is an apparent reference to an alleged incident in 1988 in which fans went into the sea as supporters of the two clubs clashed on a beach.
However, the FA have now decided no punishment is necessary.
An FA spokesman said: "Following an investigation, the FA has reminded Jonjo Shelvey of his responsibilities. No further action will follow."