Perhaps slightly high. Does it smell musty at all (I guess if it is unfinished it probably does)? Any evidence of mold?
A lot of people use the 30 per cent to 50 per cent relative humidity rule of thumb. A lot can depend of if you see any symptoms of too much or too little.
Considering your basement isn't finished it's less of a concern I would think.
If you have central A/C you may want to consider checking to see if you have both a supply and a return vent down there. Considering you basement isn't finished I doubt you have AC down there though, so this is really more of an overall tip, not necessarily for you.
If you have any electronic devices down there it is certainly too high.