Najib, who is Umno president, said in his policy speech at the annual meeting that the Act would also be enforced against those who called for the secession of Sabah and Sarawak from Malaysia.
"Having consulted with party leaders, including my deputy, vice-presidents, NGOs and the grassroots, as the Prime Minister, I have taken the decision to retain the Sedition Act.
"Do you agree?" he asked the delegates who stood up and gave him a resounding applause.
"I have analysed the Act and found that two provisions are not there. Firstly, the further preservation of the sanctity of Islam as the official religion and also prohibiting other religions from being insulted.
"Secondly, we will also include that action can be taken against those who insinuate that Sabah and Sarawak should leave Malaysia.
"Sabah, do you agree?" he said to further applause and cheers from the crowd.
The Prime Minister assured Malaysians that the enforcement of the act would be fair to ensure a more stable, peaceful, and harmonious nation for all.
Before he made the announcement, a video footage with clips of seditious postings by bloggers, social activist Hishammuddin Rais making a speech and sex blogger Alvin Tan's bak kut ten greetings was shown to the delegates.