Can rental income losses be considered a passive loss when selling the property?

Unless you have qualified and elected to be treated as a real estate professional for income tax purposes, rental losses are, by definition, passive activity losses. These losses are subject to various limitations, so some or all may be suspended in any given tax year.

At the time of complete disposition of the rental property, the taxpayer may take any suspended losses against his ordinary income for that year.

See IRS Publication 925, Passive Activity and At-Risk Rules, and Publication 527, Residential Rental Property, for further information.