Whether it is positive or negative. feedback is always meant to help.
Feedback (whether solicited or not) is common in the workplace. In addition to more formal appraisals, people will often just voice their opinion.
Receiving positive and negative feedback well is a talent we all need to sharpen. Be open to feedback, and actually listen to what you are being told. If you feel that it is a constructive conversation (not someone simply spouting off or venting) ask for clarification if necessary.
Your effort and time should be focused on working on any concerns; clarity will help you improve and learn from the feedback given.
To grow and develop you need to be receptive to feedback of all types.