The ban extends to people who have been in South Africa, Botswana, Namibia, Zimbabwe, Lesotho, Mozambique, Eswatini or Nigeria in the past 14 days.
Delegates attending G20 meetings, which Indonesia chairs, will not be affected.
First discovered in South Africa, Omicron has since been recorded in the Netherlands, Denmark, Belgium, Botswana, Germany, Hong Kong, Israel, Italy and the United Kingdom.
The discovery of Omicron, dubbed a “variant of concern” on Friday by the World Health Organization, sparked worries that it could resist vaccines and prolong the nearly two-year COVID pandemic.
Omicron is potentially more contagious than previous variants, but experts do not know yet if it will cause more or less severe COVID-19.
Countries have imposed a wave of travel bans or curbs on southern Africa. In the most far-reaching effort to keep the variant at bay, Israel announced late on Saturday it would ban the entry of all foreigners and reintroduce counterterrorism phone-tracking technology to contain the spread of the variant.