Lucius Calpurnius Piso Frugi (died 261) was a Roman usurper, whose existence is questionable, as based only on the unreliable Historia Augusta.
His name was Piso, and is said to be descendant of the gens Calpurnia and that he received the title Frugi for his severe virtues; he also possibly received the title Thessalicus.
After the death of Valerian at the hands of the Persians, his successor, Emperor Gallienus, sent Valens to suppress the rebellion of the Macriani in the east. According to the Historia Augusta, Piso was sent by Macrianus (whether he was the elder or younger is not clear) to Achaea in Greece to kill Valens. Instead, Piso withdrew to Thessaly, where he proclaimed himself emperor and was eventually killed by soldiers of Valens.