While contemporary models of psychosis have proposed a number of putative psychological mechanisms, how these impact on individuals to increase intensity of psychotic experiences in real life, outside the research laboratory, remains unclear. We aimed to investigate whether elevated stress sensitivity, experiences of aberrant novelty and salience, and enhanced anticipation of threat contribute to the development of psychotic experiences in daily life. We used the Experience Sampling Method (ESM) to assess stress, negative affect, aberrant salience, threat anticipation, and psychotic experiences in 51 individuals with First-Episode Psychosis (FEP), 46 individuals with an At-Risk Mental State (ARMS) for psychosis, and 53 controls with no personal or family history of psychosis. Linear mixed models were used to account for the multilevel structure of ESM data. In all three groups, elevated stress sensitivity, aberrant salience, and enhanced threat anticipation were associated with an increased intensity of psychotic experiences. However, elevated sensitivity to minor stressful events (χ2=6.3, p=0.044), activities (χ2=6.7, p=0.036), and areas (χ2=9.4, p=0.009) and enhanced threat anticipation (χ2=9.3, p=0.009) were associated with more intense psychotic experiences in FEP individuals than controls. Sensitivity to outsider status (χ2=5.7, p=0.058) and aberrantly salient experiences (χ2=12.3, p=0.002) were more strongly associated with psychotic experiences in ARMS individuals than controls. Our findings suggest that stress sensitivity, aberrant salience, and threat anticipation are important psychological processes in the development of psychotic experiences in daily life in the early stages of the disorder.