please, can someone tell me what this means?

ben seni biraz deyil

Many thanks,

Without context it makes no sense as there is no verb in the sentence..

Let me make up a dialogue (in which there is a verb) to see what meaning it may have:

A. Doğrusu seni özledim -- to tell you the truth I miss you

A. Biraz -- A bit

B. Sadece biraz mı? -- just a bit?

B. Ben seni biraz değil (ama çok özledim)-- I (miss) you (a lot) but not a bit 

You can use some another verb and see the result.. 

Many thanks Scalpel, you are perfectly right. I did not know that the following text

çok çok özledim

belongs to that.

Many many thansk, your intuitions is absolutely great!

Çok teşekkür ederim