You may have the Service Search for Public Service (PS) set for Search with Scan. You need to go to Menu, Search For, and Edit Search. You will see PS in the list. Press PS and you will see that Search with Scan is an option. When you press Search with Scan, go to Set Lockout. By default that should be set to Lockout. If you purchased the scanner already used from somebody, this feature may have been already set, a QK assigned, and set to Unlocked. If no QK is assigned, the scanner will still search through PS when your scanning unless it is set to Lockout. This is true for any Search or Custom Search.
That should I see this is your first post to Radio Reference. The BCT15X is a good scanner but can be complicated when first learning to use.
There is an Easy to Read Manual for the BCT15X at the website below. I suggest that you use this as a reference.
Easier to Read BCT15-X Scanner Manual