withdrawal from retirement plan & tax

Hi

I've just turned 60, and want to withdraw a certain amount of money from my retirement plan on a monthly basis. I understand I'm supposed to pay the federal and state taxes in advance (a bit over 20% of the withdrawn money.) because it's a company-sponsored plan. 

Now, this is my question:

For example, if I withdraw $2500 every month this year, the actual money I receive would be a bit over 1900 after the taxes.  Is this money ($2500 x 12=30,000) regarded as my annual income, and do I have to pay the taxes again next year during the tax-filing season? Or is it separate from my actual income from working? 

Thanks for your advice in advance.