There has been a long history of political unrest in Africa, dating back at least to the 1950s and 1960s when African countries started to gain their independence. There are at least two different main kinds of political unrest today.
The first kind of political unrest that we see today is between factions that are vying to take control of a government. In some countries, the factions are religious. An example of this is in Nigeria where the Islamist group Boko Haram wants more control over its part of the country and is fighting against largely Christian opposition. In other countries, the factions are ethnic. An example of this is in Kenya where there have been instances of violence between ethnic groups after elections.
The second kind of political unrest that we see is between authoritarian governments and the people who wish to overthrow them. We have seen examples of this in Northern Africa in the last few years. This was behind the political unrest in Libya, in Tunisia, and in Egypt.
With African countries having become independent rather recently, their political systems have in many cases not become settled yet. This has led to various kinds of political unrest in the continent.