They were convicted on terror charges by a military court for their roles in several attacks in Cameroon’s northern region which borders Nigeria.
Cameroon passed an anti-terror law in 2014 which introduced the death sentence.
This is the first time the death sentenced has been used since that law was passed.
The 89 are among 850 people arrested in Cameroon on charges of links to Boko Haram.
Following the death sentences, a local human rights group has called for reforms to Cameroon’s justice system.
Hundreds of people have been killed in a spate of attacks in Cameroon since it joined a regional force set up to tackle the militants last year.