Tag which doesn't exist?!

https://noks.rs/?wpsc_product_category=slavine

On the right side there is search form and for “Cena” (That is Price for artical, on Serbian) there are 3 tags. One of them is unexisting, “5310”, and I am wonder how to remove it. Through dashboard option Post Tags I could find no even one tag even if I set in options to show 1000 tags.

What am I supposed to do?

Thanks in advance, kind regards,

Ivan