The average cost-per-click of a Google ad decreased 9% over the first quarter of 2013 and the aggregate paid clicks decreased by around 1% over the fourth quarter of 2013.
Nevertheless, the company still saw revenues for the quarter ending 31 March increase 19% year-on-year to $15.4bn, while its year-on-year profits increased 3% to $3.45bn.
Google traditionally made extremely lucrative profit margins on desktop advertising, but is struggling to monetise mobile advertising as effectively and keep pace with Facebook, which now sees over half of its ad revenues come from mobile.
Figures from eMarketer show that Google took 49.3% of the worldwide mobile ad market last year, down from a 52.59% share in 2012.
In contrast, Facebook accounted for a 17.53% share of worldwide mobile ad spending in 2013, which was up from a 5.37% share in 2012.
Jon Myers, VP and managing director EMEA at ad tech company Marin Software, said: "The mobile search ads division is Google’s second largest and makes up approximately 29% of its total value.
"Based on the current rate of growth we predict mobile devices will account for 50% of all paid-search clicks globally by December 2015.
"For advertisers to benefit from this unstoppable trend they need to accommodate the ‘always-connected’ British consumer, who’s constantly on the go and whose shopping and product research behaviour is vastly different to anything we’ve seen before."
The UK remains Google’s key international market and its revenues from the UK totalled $1.58bn, which represents 10% of the total revenues it made in the first quarter of 2014.
In a statement, Google chief executive Larry Page said: "We completed another great quarter. Google's revenue was $15.4 billion, up 19% year on year.
"We got lots of product improvements done, especially on mobile. I'm also excited with progress on our emerging businesses."