Step by step how-to install mongo on CentOS 6.4 in right way
Lets create new repo file
sudo vi /etc/yum.repos.d/10gen.repo
Put there

[10gen]
name=10gen Repository
baseurl=http://downloads-distro.mongodb.org/repo/redhat/os/x86_64
gpgcheck=0
enabled=1

Then

sudo yum update

and

yum install mongo-10gen mongo-10gen-server

After all we have installed mongodb on centos 6.4