Nas is great at a lot of things ... rapping, feuding ... but paying taxes isn't one of them ... and now he's on the hook for another $339,000 he allegedly kept from Uncle Sam.

According to official documents obtained by TMZ, Nas never forked over $339,005.49 in federal income tax he owed for 2010 ... and now the U.S. government has obtained a lien on his property.

Being a tax scofflaw is nothing new for Nas ... according to public records, dude is also on the hook for more than $6 MILLION DOLLARS in back taxes from previous years.

We called Nas for comment -- so far, no response.

Source: TMZ

I dunno if I'm buying that especially considering the source.

If one owes $6,000,0000 in back taxes I would think they'd be incarcerated. Hell Wesley Snipes is in prison for back taxes and Willie Nelson and Sammy Davis Jr. had their property auctioned off to pay Uncle Sam.

Amazing how these entertainers always end up in tax debt and politicians like Mitt Romney get refunds.