Those market participants expecting an end to the European Central Bank's stimulus program in September could be mistaken, according to a member of the central bank's Governing Council.

Finland's Central Bank Governor Erkki Liikanen left the door open to an eventual extension to the ECB's trillion-euro stimulus package, citing political risks as a potential problem for the economic recovery in the region.

"We have been careful in our communication," Liikanen told CNBC in Helsinki. "We said we're extending net asset purchases until September and beyond if needed."

"And our monetary policy is and will be data dependent. So we must follow fresh incoming data every time," Liikanen said, adding, "We will see," when asked about a potential continuation of its asset purchases.

The ECB introduced a massive bond-buying scheme, alongside ultra-low interest rates, following the euro zone debt crisis of 2011 in order to stimulate lending and boost growth. At the end of 2017, the euro zone's central bank reduced the level of its monthly asset purchases but said it would continue to buy bonds until September of this year. At the moment, the ECB is buying 30 billion euros ($37 billion) of assets every month. But with growth and inflation expectations picking up in the euro zone, many analysts are projecting an end to the stimulus program in September and a first rate hike at some point in 2019.

In fact, the ECB dropped its so-called "easing bias" from its regular communication in early March — this used to indicate that the bank can raise and prolong the bond purchases in case of economic turmoil. This decision clearly showed the ECB sees an improvement in the euro zone.

Nonetheless, according to Liikanen, the markets should not expect any changes to the ECB's communication on future interest rates "soon."

"I wouldn't say soon, but of course the logic is that if the economy will be stronger and more convergence will take place, the role of the net asset purchase program will be smaller. And at the same time the other three elements will gain more importance especially forward guidance," the Finnish member of the ECB's Governing Council said about the different tools that the ECB has available.

He guaranteed that "there will be no abrupt sudden changes even if one day the net purchases will be finished." "But of course downside risk is mainly political. We must follow that attentively," Liikanen told CNBC.

At the ECB's January meeting, policymakers agreed that it was too early to make changes to the current level of stimulus, but admitted there could be changes in "early" 2018. Liikanen also said that the June meeting will be "important," given that the bank will have new macroeconomic forecasts and there will be further clarity on certain political issues.

"We will know more in June than what we know today."