The spokesman, Rashid Qureshi, would not say if Musharraf would announce that he is stepping down or offer any details of the planned speech, which was expected around 1 p.m. local time.
Despite mounting calls for his exit, and plans by the ruling coalition to bring an impeachment motion to Parliament this week, the longtime U.S.-backed president has so far resisted quitting.
On Sunday, a committee of the ruling coalition finalized a list of impeachment charges against Musharraf after five days of talks, Information Minister Sherry Rehman said.
Allies and rivals of the president have confirmed that backchannel talks have been underway aimed at avoiding an impeachment process.
Some current and former supporters have suggested that Musharraf might resign in return for guarantees he will not be prosecuted or forced into exile, and officials say Western and Arab emissaries have been in talks with the main parties.