If you're talking about by land area, then yes, but I'm not sure if you're talking about by where most people lived. Obviously nomadic bushmen on the savannah or pygmies deep in the jungle didn't have a civilisation or writing, but the number of people who actually lived in societies like that wasn't very high; the population of Africa didn't surpass Europe's until the 1990s, and even today there are countries like Namibia and Botswana with only a couple of million people each since they're mostly inhospitable desert.
There were plenty of societies in Africa who couldn't write, but societies like that existed in various places, from the Eskimos in the Arctic to the Australian Aborigines. There's nothing specifically African about them, other than that Africa has a lot of inhospitable desert and jungle where civilisation wasn't viable at the time.
And, yes, they did. Both the east coast of Africa and the area around the Niger river became literate due to the spread of Islamic conquerors and traders in the middle ages, and they brought Arabic or Arabic-inspired writing with them.