Comando abaixo verifica antes de subir o epel:

yum repolist
repo id repo name status
base CentOS-6 – Base 6,294
extras CentOS-6 – Extras 4
updates CentOS-6 – Updates 830
repolist: 7,128

Fazer um wget da listagem
wget http://download3.fedora.redhat.com/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
Obs: Verificar a versão mais atual em http://download3.fedora.redhat.com/pub/epel/6/x86_64/ buscando por epel-release

Adicionar:
rpm -ivh epel-release-6-8.noarch.rpm

Verificar se a chave teve sucesso na instalação:
# rpm -qa gpg*
gpg-pubkey-0608b895-4bd22942
Now install the epel-release-6-6.noarch package, which will enable EPEL repository on your system.

# rpm -ivh epel-release-6-5.noarch.rpm
Preparing… ########################################### [100%]
1:epel-release-6-5.noarch########################################### [100%]

Comparar a primeira saída observando o epel adicionado:
yum repolist