A few senators took part in the Pisonian conspiracy; many supported Nero.
From Miriam Griffin, Nero:
The cast of characters included senators, equites, praetorian tribunes, centurions and eventually one of the Prefects… The plan was modelled closely on that of the murder of Caesar: the senator Plautius Lateranus, who had earlier enjoyed Nero’s clemency, was to present a petition to the Emperor, and by grasping his knees, prevent him from avoiding the daggers of the others…In the event the scheme was a dismal failure. It foundered on the disloyalty of a freedman of the senator Flavius Scaevinus, who reported his patron’s suspicious preparations to the Emperors… According to Tacitus, many innocent men were punished on inadequate evidence… some because they were falsely accused by conspirators trying to help themselves by giving information. Yet Nero had powerful support in uncovering the plot: the consular Petronius Turpilianus, the praetor-designate Cocceius Nerva, the loyal Prefect Tigellinus and the imperial freedman Epaphroditus all received honours befitting a military victory... It was only later in 65, after the death of Poppaea and her unborn child, that the unprovoked persecution of influential senators on treason charges began in earnest.