Prevent iMac to automatically connect to Audio Receiver via Bluetooth

Hello,

I have a annoying problem with Bluetooth since upgrading my iMac to to Yosemite 10.10.3

I have a Denon AVR-S700 Audio Receiver with integrated Bluetooth. I use it for my Samsung TV (S8000 series) to wire the sound to my speakers. However, since upgrading my iMac to Yosemite 10.10.3, every time I surf the web and there is a video or animated publicity with sound, my iMac automatically connects to my Denon receiver and take over it to play the sound even if I'm watching TV. This is awfully annoying since I can't watch TV and surf the web on same time. Also, if my Denon is closed and I open my iMac, it will automatically connect to my Denon and open it.

So, in simple terms, how can I prevent my iMac to automatically connect to my audio receiver via Bluetooth?

Thank you,

Slavica