An arduino board is based on a AVR microcontroller chip and when the board with nothing wired or attached to it consumes around 80ma of 5 volt current, and that includes the 8U2 USB chip, the power on led, and other components on the board. The AVR chip is clocking at 16Mhz continuously no matter what the code is doing, it never 'halts' so it's current consumption is basically independent of the code you have it execute. Only if you put the AVR chip into one of it's 'sleep modes' can you halt code execution and drastically cut current consumption for the AVR chip, however the rest of the other components on the Uno will continue to draw their normal current consumption. Also the Arduino does not provide any 'sleep mode' examples so you will have to look for other user supplied coding example or read the AVR datasheet and figure out how to do it on your own.
Lefty