How can I know if my conv1D model is overfitted or underfitted from loss curve?
From the curves you are showing yes. Over-fitting would mean that your validation accuracy would be lower than your training accuracy, which is not the case here. Since you say that your training and validation sets are completely independent (i.e. no training samples are present in the validation set) you can consider the results reliable.

However accuracy might not be the best indicator of the model's performance. Make sure your dataset is balanced (i.e. the number of samples in both classes are equal to one another). If not try another metric that better represents the performance of your model.