Nowadays, plant-based fermented products are attracting a lot of consumer interest due to their probiotic and health-promoting properties. The aim of this study was to evaluate the microbiological quality and antioxidant activity of innovative fermented oat beverages with the addition of extracts and freeze-dried local fruit. In the first step, chokeberry and hawthorn were selected based on their antioxidant and antimicrobial properties. The final study material consisted of oat beverages fermented with the use of the Lactiplantibacillus plantarum DKK 003 strain for 20 h with the addition of 1 and 5% of extracts and freeze-dried fruits. It was found that freeze-dried chokeberry and chokeberry extracts showed a higher content of polyphenolic compounds than freeze-dried hawthorn and hawthorn extracts. After the fermentation process of the innovative beverages, the content of polyphenolic compounds remained the same or there was a slight decrease depending on the additive type. Antioxidant activity significantly decreased after 20 h of fermentation in all enriched oat beverages with no significant differences observed compared to control samples. The obtained fermented beverages were characterised by a high lactic acid bacteria count (above 8 log CFU/mL), a low pH (approximately 4.15), and no microbiological contamination. Oat fermented beverages with fruit additives can be good dietary enrichment products.