Focusing on civic engagement, as a driving force of sustainability in knowledge-based economy, the present study seeks to understand how social trust, on one hand, and conspiracy mentality, on the other hand, are influencing online (versus offline) civic actions, as well as their impact on the overall civic engagement seen as a cumulus of both attitudes and behaviours. Following literature indications, research hypotheses are developed and analysed using a questionnaire-based survey and a convenience sample for data collection. The investigation is placed in the context of an Eastern European country, and SPSS statistics package and regression analysis are used for assumptions testing and results reporting. The results indicate social trust has significant positive effects on both online and offline civic actions, while the conspiracy mentality influences mainly the online ones. The result highlights the important role of online networking in spreading and strengthening positive attitudes, but also conspiracy ideas, a higher increase in conspiracy mentality being related with participants preference for the online (versus offline) forms of involvement in civic related activities. The main contribution of the study refers to conspiracy related forms of online civic engagement, and it shows that such online actions are more related with conspiracy mentality than the offline ones, highlighting that nowadays society, which provides and consume mainly online content, is much more exposed to conspiratorial thinking than it used to be in the past. Therefore, our study indicates that although the effects of online engagement on civic participation are mostly positive, the negative influence of conspiracy believers in the online area should be addressed applying adapted knowledge management instruments that would provide the actors with adequate frames of reference, insights and knowledge about events. Since a positive civic engagement represents an indisputable social desideratum, our results might indicate an important direction of action for enabling citizens to get relevant information from their social networks and for developing effective public policies directed towards supporting civic minded citizenship and NGOs ability to provide relevant and time-ready information through social networks.