As can be seen in the following clip from the Revenge of the Sith, a group of Jedi Masters led by Mace Windu, waltz right into Chancellor Palpatine's office completely unchallenged. Then they
proceed to attack the Chancellor and all except Mace Windu are swiftly defeated as the Chancellor is actually Darth Sidius.
What is not seen in the clip is the Chancellor's personal guard, which as a head of state he must have had one. This begs the question of where were they at that moment?
Later on we see that
(now Emperor) Palpatine actually has a guard, who however are swiftly defeated by Yoda.