Do you file a federal return if you only get social security and a monthly pension check of 259.00

You need to file a federal return if half your Social Security plus your other income is $25,000 when filing single or head of household, or $32,000 when filing married filing jointly, $0 if you are filing married filing separately.

Who has to file?

http://www.irs.gov/uac/Do-I-Need-to-File-a-Tax-Return%3F

If that is your only income there is no reason to file a federal tax return since your taxable income would be below the Standard Deduction for your filing status.

However, if you have health care insurance through one of the state Marketplace Exchanges or from healthcare.gov and receive a Form 1095-A then you will have to file a federal tax return.

Are you single?   You don't have to file if you get under 13,850 (15,700 if over 65) not counting Social Security.  Unless the pension or ss take out withholding.   

Do you need to file a return?

https://ttlc.intuit.com/community/filing-and-paying-taxes/help/do-i-need-to-file-a-federal-return-this-year/00/25546

IRS Do I need to file?

Do I Need to File a Tax Return? | Internal Revenue Service