Can I listen to music from Imac late 2009 running mountain lion?

Yes, you can.
Your iMac has bluetooth technology built-in.

Here are the specs for your Mac from Apple's website.

Communications
Built-in AirPort Extreme Wi-Fi wireless networking (based on IEEE 802.11n draft specification);2 IEEE 802.11a/b/g compatible
Built-in Bluetooth 2.1 + EDR (Enhanced Data Rate)
Built-in 10/100/1000BASE-T Gigabit Ethernet (RJ-45 connector)

• Answered by Andres Jr T from Yuma
• 23-Dec-2012
• Flag as inappropriate