Napster allows streaming in one location at a time.

If you use your account to stream music from two places at once, like from a phone and also from Napster's website at the same time, you'll get the message "Account in Use: Your Napster account is now streaming music in another location, and this session will end" or "It looks like your Napster account is being used in another location. Click OK to continue."

To avoid these messages, download music to your iPhone, iPad, Android or Windows Phone with our mobile app and then listen in offline or airplane mode. Listening to downloaded music offline in one location while streaming music in another location prevents these messages.

See steps for downloading music here.