Nope, it's not charging. Normal running voltage against a fully charged battery needs to be 14.5 or slightly higher. It sounds like your alternator has at least one leaky diode that allows a parasitic drain of the battery- - - -a small constant current that drains the battery over the span of a few days, or maybe weeks. If you run the engine regularly, does the battery stay charged? You can check for parasitic drain a couple of ways- - - -disconnect the big output lead at the alternator and leave it loose for a week. Check to see if the battery stays up. If so, change the alternator. Another method is to disconnect the same lead and use the "ammeter" section of a digital multimeter to check for current leakage. More than a few milliamps of parasitic drain is too much.
You could also have some other item causing a drain. The constant voltage "keep alive" circuit on a sound system like a CD player, etc. will drain a battery over a span of several weeks if the engine isn't run occasionally.
Jerry
