Mobile represented 69% of total Facebook ad revenue in Q4 2014

"Full Year 2014 Business Highlights
Revenue for the full year 2014 was $12.47 billion, an increase of 58% year-over-year.
Income from operations for the full year 2014 was $4.99 billion.
Net income for the full year 2014 was $2.94 billion.
Free cash flow for the full year 2014 was $3.63 billion.
Daily active users (DAUs) were 890 million on average for December 2014, an increase of 18% year-over-year.
Mobile DAUs were 745 million on average for December 2014, an increase of 34% year-over-year.
Monthly active users (MAUs) were 1.39 billion as of December 31, 2014, an increase of 13% year-over-year.
Mobile MAUs were 1.19 billion as of December 31, 2014, an increase of 26% year-over-year.
Revenue - Revenue for the fourth quarter of 2014 totaled $3.85 billion, an increase of 49%, compared with $2.59 billion in the fourth quarter of 2013. Excluding the impact of year-over-year changes in foreign exchange rates, revenue would have increased by 53%.
Revenue from advertising was $3.59 billion, a 53% increase from the same quarter last year. Excluding the impact of year-over-year changes in foreign exchange rates, revenue from advertising would have increased by 58%.
Mobile advertising revenue represented approximately 69% of advertising revenue for the fourth quarter of 2014, up from approximately 53% of advertising revenue in the fourth quarter of 2013.
Payments and other fees revenue was $257 million, a 7% increase from the same quarter last year."
Source:  Facebook's 4th Quarter & full year 2014 Results, 28th January 2015
See charts of some of the data here