DIAGNOSIS The microphone is physically muted (the button is pressed in), but a communication glitch with the Alexa service is keeping the "active" indicator lit. It's a software state error.
FIX Perform a full power cycle. Unplug the power adapter from the electrical outlet, not just from the speaker. Wait 60 seconds. Plug it back in. When the light ring does its startup sequence, it should settle to off (or a brief pulse when muted).
IF THAT DIDN'T WORK Toggle the mute state. Press the microphone mute button on top to turn the mics on (light ring should turn red). Wait 10 seconds, then press it again to turn the mics back off (light should go out). This resets the internal mute circuit.
HEADS UP A solid blue light when not in use indicates it thinks it's in a call or Drop In. Say "Alexa, hang up" just in case. If the light persists after all this, it may indicate a failing light ring module, which requires service.