A believer is an advocate who supports what he finds and fan as fact and truth.
A follower is one who obeys and follows what he believes as fact and truth.
A Believer may not necessarily a follower but a follower is a believer that advocates, obeys, follows and stands trusting belief as conviction and explaining conviction as faith hence footing the faith from belief to confidence making unseen idea as a seen confidence;
In reality and as scope the same is the theme in sacrifice where a martyr rolls around his belief sacrificing life in conviction as faith.
In My opinion, a believer can be a Muslim or non-Muslim but a follower has the credentials of Muslim only making dominion of religion particularly as the only domain of those who believes follows and sacrifices their lives and assets for what they believe in. (Dr raza)
[2:105] احمد علی
اہل کتاب کے کافر اور مشرک نہیں چاہتے کہ تمہارے رب کی طرف سے تم پر کوئی بھی اچھی بات نازل ہو اور الله اپنی رحمت کے ساتھ خاص کر لیتا ہے جسے چاہے اور الله بڑے فضل والا ہے