Stewart plays Bella Swan in the vampire series, while Mulligan starred in the Golden Globe-nominated An Education.
Skins star Nicholas Hoult, French actor Tahar Rahim and US actor Jessie Eisenberg are also up for the prize, which recognises emerging talent.
The winner is decided by a public vote, both by text and online.
The winner of this year's award will be announced at the Bafta film awards in London on 21 February.
Source & source
Update: VOTE HERE (Only UK residents votes are taken into account)