Mo Ibrahim, the Sudan-born telecoms tycoon, who founded the Ibrahim Index of African Governance, said overall governance had improved on the continent over the past five years, though all the leading countries have seen reverses in some fields.
Mauritius remains top of the 52 countries ranked, while Somalia stays far adrift at the bottom of the table.
The index ranks 52 countries according to 95 indicators grouped under four categories: safety and the rule of law, participation and human rights, sustainable economic opportunity and human development.
Egypt and Libya, two countries shaken by Arab Spring revolutions, have fallen the furthest in the rankings, while Tunisia, which started the wave of revolutions, has remained relatively stable.
Egypt has shown the biggest deterioration in overall governance over the past five years, dropping eight points to 51.1 out of 100. It is consequently down 14 places in the African rankings to 26th.
Neighbouring Libya dropped 7.4 points to 42.1, and 16 places in the rankings to 43rd.
The biggest riser in the index over the last five years has been Ivory Coast, up 7.8 points to 44.3, and rising six places in the index to 40th.
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The top five countries in the 2014 index remained the same: Mauritius (81.7), Cape Verde (76.6), Botswana (76.2), South Africa (73.3) and Seychelles (73.2).
However Ibrahim said: "Over the past five years, every one of the top five ranking countries has deteriorated in at least one category, demonstrating that even the highest performers need to remain vigilant."
The bottom five were Guinea-Bissau (33.2), Chad (32.3), Eritrea (29.8), Central African Republic (24.8) and Somalia (8.6).
Previously the index has been announced alongside the Ibrahim Prize for Achievement in African Leadership – the world's biggest individual prize.
Given to retiring good leaders, no suitable candidates have been found in four of the last five years.
The announcement was overshadowing the more meaty data charting Africa's progress, so this year the two are being unveiled separately although no date has yet been set for the leadership prize.