When Popilius speaks to Cassius, does he know about the conspiracy?

In Act III, Scene 1 of Julius Caesar, Popilius enters along with a large group of other dignitaries. Popilius in an "Aside to Cassius" says, "I wish your enterprise today may thrive." Cassius is immediately alarmed. He asks, "What enterprise, Popilius?" Popilius merely answers, "Fare you well." Then the stage directions state, "He leaves Cassius, and makes to Caesar." Brutus asks, "What said Popilius Lena?" Cassius tells him, "He wished today our enterprise might thrive....

In Act III, Scene 1 of Julius Caesar, Popilius enters along with a large group of other dignitaries. Popilius in an "Aside to Cassius" says, "I wish your enterprise today may thrive." Cassius is immediately alarmed. He asks, "What enterprise, Popilius?" Popilius merely answers, "Fare you well." Then the stage directions state, "He leaves Cassius, and makes to Caesar." Brutus asks, "What said Popilius Lena?" Cassius tells him, "He wished today our enterprise might thrive. / I fear our purpose is discovered."

It seems unlikely that Cassius could have spent so much time and energy trying to recruit men to his conspiracy without some word of his plan leaking out to other men who were either pro-Caesar or neutral. In going directly to Caesar after wishing Cassius good luck with his "enterprise," it is inferable that Popilius is looking out for his own best interests. He apparently knows about the plot against Caesar, but he may only be concerned about what will happen to him and his family whether the assassination succeeds or fails. He gives Cassius his best wishes in order to show he is on his side, and then goes straight to Julius Caesar and engages him in conversation. He is not warning Caesar, just making friendly conversation. As Brutus tells Cassius,

Cassius, be constant.
Popilius Lena speaks not of our purposes,
For look, he smiles, and Caesar does not change.

If Cassius and Brutus are successful, they will remember Popilius expressed his good wishes. If Caesar manages to thwart the assassination attempt, Popilius may be anxious to have him remember that he was behaving in such a cordial manner just before the conspirators attacked. 

Julius Caesar is feared by everyone. He might know all about the proposed assassination attempt and just be waiting to have all the conspirators arrested or killed on the spot. Popilius could be maneuvering to be on the winning side, regardless of which side wins. It is likely that other men know about the plot and hope to stay neutral in order to avoid the blood bath they would naturally expect to occur if Brutus and Cassius came out on top or if Caesar prevailed and went on to claim his crown. We see that Antony, Octavius, and Lepidus stage a blood bath when they emerge as the final victors, but Brutus is too high-principled to allow the same thing to happen during the short time he and his followers hold the power in Rome.

When Antony, Octavius, and Lepidus make a list of the men who are to be purged in Act IV, Scene 1, there is no mention of Popilius. In Act IV, Scene 2, when Brutus, Cassius, and Messala are talking about about the blood bath staged by Antony, Octavius, and Lepidus, Popilius is not mentioned. Even if Brutus and Cassius were to have staged their own blood bath after assassinating Caesar, they would not have included Popilius in their purge because, although he knew about their plot, he didn't warn Caesar. Popilius's brief appearance in Act III, Scene 1 serves to heighten the suspense and suggest the plausible danger that other men in the crowd know about the time and place of the assassination attempt and that Julius Caesar could therefore know about it himself!