This is considered a job-related expense.
To claim this you must be able to itemized and the job-related expenses must exceed 2% of your adjusted gross income. So for example, if the income is $75K, then the job related must exceed $1,500 before it starts to impact your taxes.
To deduct this go to:
Federal Taxes (Personal of using Self-employed)
to Deductions and Credits
scroll down to Employment Expenses, then to Job-Related Expenses
It will walk through the Office in the Home expenses for you.