Top performers are Benin, Burkina Faso, Ethiopia, Ghana, Ivory Coast, Rwanda, Senegal and Tanzania, the International Monetary Fund said.
Their economies expanded by six percent or more in 2017 and will maintain strong growth over the medium term, it said.
The star is Ethiopia, which notched up 10.9 percent growth in gross domestic product (GDP) in 2017, and is expected to enjoy 8.5 percent this year.
At the other end of the scale lie 12 countries, home to about a third of sub-Saharan Africa's population.
Last year, per-capita incomes declined in these economies -- a trend that is likely to happen in most of them in 2018, it said.
Its Regional Economic Outlook for 2018 praised high-performing countries that have tackled entrenched macro-economic problems and encouraged investment.
These economies have also benefited from favourable global winds -- stronger world growth and higher commodities prices.
As a result, capital inflows in these economies have risen, and some countries have been able to build up their reserves.
For the laggards, though, much of the pain lies from the failure to address spending, remove market-distorting policies and mobilise capital.
"Macroeconomic vulnerabilities are rising in many countries as the required fiscal adjustment keeps getting delayed," Abebe Aemro Selassie, director of the IMF's African Department, said in a press release.
"Fifteen of the region's 35 low-income countries are now rated to be in debt distress or at high risk of debt distress," he warned.