EAP SSL Cert "Not Trusted"

Hello, We have several freeradius servers with a valid certificate for EAP. When the clients first log in via wifi, they are presented with a certificate "Not Trusted" warning, even though that certificate is signed by a trusted CA. Is this the expected behavior? Is this because we are missing a piece that is required by the client to trust this certificate? Awhile ago someone said that this should happen that the user should get the cert warning, thus this would occur every time the certificate is renewed. Cheers, - Trevor